Processes for using bastnaesite/metal oxide compounds

ABSTRACT

Bastnaesite materials and Mg A! (and/or Al B!) materials can be chemically reacted by use of reactions wherein a Al B! ingredient such as alumina is made into a sol by use of a mono-protonic acid before Mg A! (and/or Al B!) materials is (are) reacted with the bastnaesite material. The resulting compounds are then used as SO x  catalyst/absorbent materials in fluid catalytic cracking units and/or in fixed bed units.

RELATED APPLICATIONS

This patent application is a continuation-in-part application of U.S.patent application Ser. No. 08/099,828 filed Jul. 30, 1993 entitled"Processes for Reacting Bastnaesite with Metal Oxides, now U.S. Pat. No.5,422,332 issued Jun. 6, 1995."

FIELD OF THE INVENTION

This invention is generally concerned with chemically reactingbastnaesite with bivalent and/or trivalent metal oxides and using theresulting compounds as SO_(x) absorbent/catalyst materials.

BACKGROUND OF THE INVENTION Re: Bastnaesite

Generally speaking, the term "bastnaesite" denotes a group of mineralswhich can be regarded as being comprised of fluorocarbonates of certainrare earth metals. However, the nomenclature used to describe suchmaterials is often rather vague. For example, since the chief componentsof bastnaesite are the "rare earths", such materials are sometimesreferred to as rare earth oxides. These materials also are commonlyreferred to as "lanthanides". This term is obviously a corruption of theword lanthanum, which of course is the first member (or lowest atomicnumber member) of the lanthanide group in the periodic table. Thosefamiliar with this art also will appreciate that it is not at all anuncommon practice to use the symbol for the lanthanides ("Ln") togenerally denote all of the lanthanides when they are considered as agroup. Similarly, it also is common practice to refer to the variousoxides of the entire lanthanide group as LnO--and to their oxyflouridesas LnOF. Given all of these considerations, it is quite common todesignate the chemical makeup of bastnaesites, in general, by theformula: (Ce,La)OF, even though such materials contain many otherelements. For example, mineral bastnaesite contains from about 65 toabout 80% by weight of assorted rare earth elements (calculated as rareearth oxides) with its primary metallic components being lanthanum andcerium. This fact explains the widespread use of (Ce,La)OF as thechemical formula for these materials. However, bastnaesite mineralsalmost always contain small proportions of various other rare earthelements such as praseodymium, neodymium, samarium, europium, andgadolinium. For example, chemical analysis of a typical bastnaesitemineral might show proportions of individual rare earth elements(calculated as oxides) to the total rare earth elements (also calculatedas oxides) which fall within the general ranges: 45 to 55 wt. % CeO₂, 29to 35 wt. % La₂ O₃, 11 to 15 wt. % Nd₂ O₃, 2.5 to 5.5 wt. % Pr₂ O₃, 0.3to 0.7 wt. % Sm₂ O₃, 0.1 to 0.3 wt. % Gd₂ O₃, 0.05 to 0.15 wt. % Eu₂ O₃and 0.05 to 0.35 wt. % of other rare earth elements.

Next, it should be noted that bastnaesite is a somewhat chemicallyreactive mineral. Consequently, it can be modified by relativelymoderate chemical and/or physical treatment processes such as steaming,calcining and acid leaching. For instance, when naturally occurringbastnaesite is calcined in air at a temperature around 700° C., itundergoes a chemical reaction wherein some of its rare earthfluorocarbonates are converted to rare earth oxyfluorides. By way ofanother example of such modifications, mineral bastnaesite can beleached with certain strong acids in order to withdraw its strontium andbarium content. Be all of this as it may, this invention contemplatesuse of either naturally occurring forms of bastnaesite or any number ofchemically and/or physically treated forms of that mineral. Hence, forthe purposes of this patent disclosure, the terms "bastnaesite","treated bastnaesite", "bastnaesite mineral(s)", "bastnaesite-likematerials" etc should be taken to include not only those raw mineralforms of bastnaesite found in nature, but also a wide variety ofphysically or chemically treated forms of bastnaesite minerals--indeed,for the purposes of this patent disclosure, these terms should even betaken to include any synthetic material having a distribution of rareearth elements to total rare earth elements substantially similar tothose of naturally occurring bastnaesite minerals.

Catalytic Uses Of Bastnaesite

Bastnaesite has an initial ability to chemically react with SO_(x) underthose conditions existing in a catalyst regeneration zone of a fluidcatalytic cracking ("FCC") unit. Consequently, bastnaesite has beenphysically associated with various hydrocarbon cracking catalysts inorder to catalyze the oxidation of SO_(x) produced by regeneration ofvarious hydrocarbon cracking catalysts. Bastnaesite also has the abilityto absorb SO₃ gas. For example, U.S. Pat. Nos. 4,366,083 (the 083patent); 4,311,581 (the 581 patent) and 4,341,661 (the 661 patent) teachSO_(x) catalytic and/or absorbance activity of bastnaesite particleswhich are circulated in physical admixture with various hydrocarboncracking catalysts. However, bastnaesite compositions have not beenwidely used as SO_(x) additive materials because there are far betterSO_(x) catalyst materials (e.g., ceria, vanadia, etc.) and becausebastnaesite is not a good long term absorbent because it is not easilyregenerated under those conditions found in a fluid catalytic crackingunit or its catalyst regenerator unit. That is to say that bastnaesitewill readily pick up SO₃ gas during the bastnaesite's first trip throughthe FCC unit, but that the SO₃ is not readily driven away from thebastnaesite during subsequent regeneration steps. Consequently, largeinitial amounts of bastnaesite (e.g., 15% of the bulk catalyst) must beused in the unit's bulk catalyst in order to maintain the ability ofsuch processes to absorb SO₃ gas--and the bastnaesite supply must becontinuously augmented. The latter procedure involves the use of largequantities of bastnaesite in the "make-up" catalyst which isintermittently supplied to the FCC unit. The resulting large proportionsof non-hydrocarbon cracking catalytic material tend to destabilize theoverall catalytic process being carried out in a FCC unit. Consequently,other materials which can be readily "regenerated" (e.g., alumina,ceria, lanthanum, etc. and alumina support materials impregnated withceria, lanthanum, etc.) have been used in preference to bastnaesite forSO₃ absorption purposes.

None of the above references, however, teach methods whereby bastnaesitecan be chemically reacted with those hydrocarbon cracking catalystmaterials with which they are physically mixed. That is to say thatunder the broadest teachings of the 083; 581 and 661 patents,bastnaesite can be employed in either of two ways: (1) bastnaesiteparticles can be admixed with separate and distinct hydrocarbon crackingcatalyst particles--that is to say that the bastnaesite particles andthe hydrocarbon cracking catalyst particles become thoroughly mixed asthey are circulated through a FCC unit--but they remain in the form ofseparate and distinct particle species or (2) bastnaesite particles canbe physically incorporated into matrices which are comprised of bothhydrocarbon cracking catalyst particles and bastnaesite particles--thatis to say that these two different kinds of particles are "glued"together by the use of binder materials in order to form a compositeparticle. For example, the 083; 581 and 661 patents teach thatcrystalline aluminosilicate zeolite hydrocarbon cracking catalysts canbe "glued" to bastnaesite particles through the use of an inorganicrefractory oxide binder material. In other words, the bastnaesiteparticles are physically dispersed in an overall particle whose matrixis comprised of bastnaesite particles, aluminosilicate zeolite particlesand the matrix binder material.

Re: Metal Oxide Materials

Various metal oxide materials such as those described in U.S. Pat. Nos.4,381,991 (the 991 patent) and 4,369,130 (the 130 patent) have beenemployed as SO_(x) absorbent/catalyst materials. In most cases thesematerials are bivalent and/or trivalent metal oxides such as those ofthe alkaline earth metals. When bivalent and trivalent oxides such asthose described in the 991 patent are combined with each other, theresulting materials are sometimes considered to be a distinct group ofmetal oxides commonly referred to as "spinels" or synthetic spinels.Indeed, the term "spinel" is often loosely used to describe a widevariety of minerals having certain metal oxide ingredients. It is alsotrue that many metal oxide materials which could be called "spinels" arenot designated by use of this term. For example, the materials producedby the process described in Example 10 of the 991 patent (at Column 22,Line 53), could legitimately be called synthetic spinels even though theterm "spinel" is not specifically used in that patent disclosure.

The term "spinel" is also used to describe a variety of naturallyoccurring minerals which contain various combinations of two or moremetal oxides wherein the metals have different valances. A more preciseuse of the term also implies metal oxide materials (mineral orsynthetic) crystallized in an isometric system with an octahedral habit.Spinels are also often thought of as combinations of bivalent andtrivalent oxides of magnesium, zinc, cerium, lanthanum, iron, manganese,aluminum, and chromium. Some of the more important mineral forms ofspinel are spinel (MgAl₂ O₄), gahnite, zinc spinel (ZnAl₂ O₄),franklinite (Zn,Mn²⁺,Fe²⁺) (Fe³⁺,Mn³⁺)₂ O₄, and chromite (FeCr₂ O₄).Spinels, in general, are frequently designated by the general formula:R²⁺ O R₂ ³⁺ O₃ wherein R is a metal having a valance of plus two and R₂is a metal having a valance of plus three. For the most part, thebivalent oxides are MgO, ZnO, FeO, and MnO. The trivalent oxides aretypically Al₂ O₃, Fe₂ O₃, Mn₂ O₃, La₂ O₃, Ce₂ O₃ and Cr₂ O₃. Of thesematerials, MgAl₂ O₄ is the most important--indeed the term "spinel" isoften taken to mean the magnesia/alumina (MgO/Al₂ O₃) form of thesematerials.

In another sense, spinels may be thought of as being comprised of afirst metal having a first oxidation state and a second metal having anoxidation state higher than that of the first metal and wherein eachmetal is appropriately associated with oxygen in a lattice structure.The first and second metals may even be the same metal. In other words,the same metal may exist in a given spinel in two or more differentoxidation states. It also should be understood that the atomic ratio ofthe first metal to the second metal in any given spinel need not beconsistent with the classical stoichiometric formula for the variouscomponents of a given spinel. Thus, in an even broader sense, spinelsmay be thought of as being composed of bivalent and trivalent metallicoxides of continuously varying proportions i.e., materials having thegeneral formula: nR²⁺ O mR³⁺ ₂ O₃ wherein the ratio of n to m may vary.Those skilled in this art will appreciate that continuously variableratios of atoms is a common occurrence in those materials known as"solid solutions."

Catalytic Uses of Metal Oxide Crystals

Metal oxide crystals such as those commonly referred to as spinels havebeen employed as catalysts in petroleum refining operations for almost50 years. However, it is of considerable importance to a properunderstanding of the scope of this patent disclosure to recognize thatthe use of such materials for catalytic purposes has had an "up anddown" evolutionary development. Originally, mineral spinels were used ascatalysts for cracking crude petroleum into various refined products.The use of mineral spinels eventually led to the use of certainsynthetic spinels. Both kinds of spinel (naturally occurring andsynthetic) were so employed because they each have relatively largenumbers of catalytically active acid sites distributed over theirextensive, porous surfaces. The petroleum industry also learned to"tailor" various synthetic spinels for certain very specific purposes.For example, spinel matrices with an excess of alumina were developedfor use in certain fluid catalytic cracking operations because thesematerials tend to have a durable, attrition-resistant character. Thisattribute follows from the fact that trivalent aluminum oxide, themineral corundum (in its natural state), is extremely hard--indeed, itis right next to diamond on Mohs' scale of hardness.

Use of naturally occurring and synthetic spinels as petroleum crackingcatalysts was, however, eventually phased out when petroleum crackingwas realized through other, more catalytically active, materials such ascrystalline aluminosilicate zeolites. This phasing out of spinels alsowas forced by purely physical considerations. For example, those MS-FCCcatalysts (micro-spheroidal, fluid catalytic cracking catalysts) whichare used in modern petroleum cracking operations must be substantiallyspherical in form. They also must be made in a rather narrow range ofsizes and densities so they can achieve uniform fluidization. It mighteven be said that FCC catalysts must be made with almost as muchattention paid to their size, shape and density as to their chemicalcomposition.

Unfortunately, these physical requirements produced several problemswith respect to the use of spinels in FCC units. Most of these problemsrevolved around the fact that spinels in general, and naturallyoccurring spinels in particular, are not of suitable size, shape, and/ordensity for use in fluidized processes. Consequently, they were easilyelutriated from an FCC unit. Such elutriation losses were veryconsiderable--and very costly. On the other hand, when spinels werephysically bound in those matrix-forming materials normally used tocreate FCC particles, the spinels tended to become much less effectiveas hydrocarbon cracking catalysts. In any event, the above-notedcatalytic and physical drawbacks prodded the petroleum refining industryinto developing more effective FCC catalysts (e.g., aluminosilicatezeolites). They were successful in these endeavors and, in time, spinelsvirtually disappeared from the petroleum cracking scene.

Interest in the use of certain crystalline metal oxides (such asspinels) as catalysts has, however, revived in more recent times. Thisnewfound interest follows from the fact that such materials, aside fromtheir petroleum cracking capabilities, also can be used to lower theconcentrations of those noxious sulfur oxides (SO_(x)), e.g., SO₂ andSO₃, which are emitted in the course of burning and/or catalyzingsulfur-containing fossil fuels and/or regenerating carbon andsulfur-contaminated hydrocarbon cracking catalysts.

In this regard, it also should be specifically noted that spinels, intheir own right, possess some SO_(x) catalytic activity; but they areeven more effective as SO₃ absorbents. That is to say thatspinels--aside from whatever SO_(x) catalytic activities they maypossess--also have the separate and distinct ability to absorb sulfurtrioxide. These distinctions are noteworthy because in order to recoversulfur from a sulfur oxide-containing gas, its SO₂ content first must beconverted to SO₃. It is only after the SO₂ is converted to SO3 that theSO₃ can be picked up by an SO_(x) absorbent--which for the most part isa SO₃ absorbent. This follows from the fact that there are noeconomically suitable materials which are capable of effectivelyabsorbing SO₂ gases. There are, however, several economically viablematerials, including spinels, which are capable of absorbing SO₃ gases.Hence, the SO₂ content of a gas stream must be oxidized to SO₃ so thatthe SO₃ can be picked up by an absorbent. In other words, it is onlyafter the SO₂ is converted to SO₃ that the undesired sulfur content of agas stream can be removed. Consequently, spinels have been physicallyassociated with various SO_(x) catalysts (e.g., cerium, vanadium,platinum, etc.) in order to perform the required SO₃ absorptionfunction. In other words, it is usually the separate and distinct SO_(x)catalyst species (e.g., cerium and/or vanadium) which, for the mostpart, serves to catalyze the oxidation of sulfur dioxide to sulfurtrioxide, while spinel serves mostly to absorb the sulfur trioxide onceit is formed through the use of such cerium or vanadium SO_(x) catalystmaterials.

Next, it should be noted that in the course of manufacturing variouscrystalline, metal oxide materials by most prior art methods, certainchemical reactions readily take place wherein various complex compoundse.g., magnesium oxide (MgO), stoichiometric spinel (MgAl₂ O₄) etc. areformed. In most prior art processes, these complex compounds are looselydistributed throughout a crystalline matrix of an excess of one of thespinel's ingredients (e.g., in an alumina matrix of a magnesia/aluminaspinel). To emphasize this point, applicant has chosen to describe andcharacterize that MgO which is "loosely" distributed in a spinel (i.e.,MgO which does not form a part of a spinel's crystalline latticestructure), by use of the expression "free magnesium oxide." For thepurpose of this patent disclosure, all such excess compounds (e.g., freemagnesium oxide, stoichiometric spinel, etc.) also may be referred to as"free, complex metal oxides".

Regardless of terminology however, this loose distribution of freecomplex metal oxides is known to impart certain properties to theresulting materials. For example, within the catalyst regeneration arts,it has long been recognized that the presence of large amounts ofloosely distributed MgO in spinels can enhance their SO_(x) absorbentand/or SO_(x) catalytic abilities. However, practitioners of these artssoon learned that when increased SO_(x) activity was pursued by creatingmagnesia/alumina spinels which are characterized by the presence ofexcess MgO, the hardness of the resulting spinel is greatly diminished.This follows from the fact that MgO is not nearly as hard as, and hencenot nearly as attrition resistant as, alumina. Consequently, under thesevere attrition and impingement conditions which are encountered influidized beds, the prior art experienced unacceptably severe and rapidbreakage (and hence loss) of those MS-FCC synthetic spinel particleswhich contain relatively large amounts of "free magnesium oxide".

Nonetheless, all such drawbacks notwithstanding, it should be noted thatany in depth review of the prior art literature dealing with the use ofmixtures of two or more metal oxides in a crystalline lattice material(acting in the capacity of SO_(x) catalysts and/or absorbents), revealsthat a "school of thought" among many workers skilled in this art haspersistently held that the presence of such complex compounds (e.g.,complex metal oxides such as free magnesia, stoichiometric spinel, etc.)is an ineluctable--and even highly desirable--attribute of thesematerials. See, for example U.S. Pat. No. 4,728,635 (the 635 patent) atcolumn 4, line 31 where use of up to 30% of such free magnesia isadvocated.

Applicant, however, very decidedly belongs to an opposing school ofthought which holds that the presence of "free" complex metal oxidessuch as free magnesium oxide, is an inherently "undesirable" attributefor those spinel or spinel-like materials used as SO_(x)absorbent/catalyst materials--and should be avoided as much as possible.That is to say that applicant is of the opinion that the SO_(x)absorbent and/or catalyst performance of the herein describedbastnaesite/metal oxide materials can be enhanced if any excess (amountsin "excess" of that implicit in the stoichiometric formula) magnesiumoxide is present as a part of a solid solution in that material's"magnesium rich" homogeneous crystalline structure--as opposed to beingpresent in the form of "free" magnesium oxide which is not so associatedwith that material's metal oxide crystalline structure.

However, it also should be noted that applicant may not be entirelyalone in some of his beliefs concerning the SO_(x) catalyzing propertiesresulting from the manner in which magnesium oxide is associated with aspinel's other chemical constituents. For example, U.S. Pat. No.4,471,070 ("the 070 patent") teaches various methods of making syntheticspinels wherein the atomic ratio of magnesium to aluminum is purposelyheld to a range of 0.17 to 1.0 in order to enhance the resultingspinel's SO_(x) catalytic activity. The point to be made here is thatthe 0.17 to 1.0 ratios could imply "magnesium rich" spinels if themagnesium to aluminum ratio is greater than 0.5 to 1.0. It also shouldbe noted that the 635 patent, in spite of its previously citedpreference for the presence of free alkaline earth metal oxides such asMgO, also teaches methods of making spinels wherein the ratio ofalkaline earth metal (e.g., Mg) to aluminum is made to fall between 0.17and 2.5. Thus, in effect, the 635 patent teaches methods for makingspinels which have both "excess" magnesium oxide as part of theirlattice structures--while simultaneously, having "free" magnesiaotherwise associated with that same spinel. Thus, in spite of the 635patent's stated preference for the presence of free magnesium oxide, itsspinels also could be characterized (using applicant's terminology), as"magnesium-rich" spinels in those cases where the material's magnesiumto aluminum ratio is greater than 0.5 to 1.

On another front, the prior art with respect to the catalytic uses ofcrystalline metal oxide materials has long recognized that certain metalions, such as those of iron, chromium, vanadium, manganese, gallium,boron, cobalt, Group IB metals, cerium Group IV metals, Group VA metals,the platinum group metals, the rare earth metals, Te, Nb, Ta, Sc, Zn, Y,Mo, W, Tl, Re, U, Th and mixtures thereof, may replace all or part ofthe aluminum ions of certain spinels. In somewhat the same vein, theprior art also has taken advantage of the fact that SO_(x) can beremoved from gases by various metal oxide absorbents when thesematerials are placed in association with at least one free or combinedrare earth metal selected from the group consisting of lanthanum,cerium, praseodymium, samarium and dysprosium. For example, it is wellknown that crystalline metal oxides and magnesium/aluminum spinels inparticular, can be physically associated with various catalyticallyactive metals by impregnating their particles with certainmetal-containing solutions (e.g., those of cerium, vanadium, platinum,etc.) and then calcining the resulting impregnated spinel particles andthereby producing even more effective SO_(x) catalysts.

Indeed, it might even be said that, to a very large degree, the priorart with respect to using crystalline, metal oxide materials such assynthetic spinels as hydrocarbon cracking catalysts and/or as SO_(x)absorbents (or catalysts) has largely focused upon finding better waysof associating various catalytically active materials (e.g., cerium,vanadium, etc.) with all manner of such crystalline metal oxidematerials in order to enhance the resulting material's SO_(x) absorbing(or catalyzing) capabilities. Representative patents teaching suchtechnologies include U.S. Pat. Nos. 4,381,991; 4,497,902; 4,405,443;4,369,130; 4,369,108; 4,233,276 and 4,325,811. Analogous SO_(x)absorption technologies also are taught in U.S. Pat. Nos. 4,423,019;3,835,031; 4,153,534; 4,238,317; 4,267,072; 4,221,677; 4,218,344;4,206,039 and 4,153,535.

As a final note regarding the prior art, applicant also would point outthat the technology described in U.S. Pat. No. 5,108,979 ("the 979patent") was developed in response to several of the abovenoted problemsassociated with the use of crystalline metal oxide materials (e.g.,spinels) as SO_(x) absorbent/catalyst materials. Indeed, the teachingsof the 979 patent represent a very convenient starting point fordescribing the present invention; hence, the 979 patent is specificallyincorporated by reference into this patent disclosure. Among otherthings, the 979 patent teaches that production of various free complexmetal oxide compounds such as free magnesium oxide and stoichiometricspinel can be avoided by manufacturing processes wherein substantiallyall of the ingredients (e.g., magnesia, alumina, etc.) are "forced" tobecome an integral part of the resulting material's regular crystallinelattice structure (as opposed to being only loosely associated with suchcrystalline structure). This forced residence in the crystallinelattices of these materials was accomplished in the processes describedin the 979 patent by production processes involving the conjunctive useof extremely small sized ingredient materials (e.g., those smaller than5 nanometers) along with the use of certain prescribed pH levels intheir initial reaction mixtures.

As a follow-up to some of the experimental work which formed the basisof the technology described in the 979 patent, applicant embarked uponan expanded experimental program aimed at physically incorporatingvarious density-imparting, but catalytically inert, ingredients intovarious spinel materials taught in that patent. A need for such measuresarose because some of the spinels produced by the processes described inthe 979 processes were not--in their own right--dense enough to achieveoptimum fluidization in certain FCC operations. Consequently, variousmaterials having densities higher than that of spinels were physicallymixed with the spinel-forming ingredients in a unified matrix in orderto raise the overall density of the resulting particles. To this end,bastnaesite was used as just such a density-raising material. In effect,the heavier bastnaesite particles and the lighter spinel particles were"glued together" in the form of a composite particle which is heldtogether by one or more catalyst binder material(s) in order that theresulting composite particles have a density better suited forfluidization.

Among other things, applicant's experimental program with respect tophysically mixing bastnaesite with various spinel-forming ingredientsserved to show that the physical presence of bastnaesite in a matrix ofsuch materials does in fact raise the overall density of a FCC particleto desirable levels--but does not, per se, improve the efficacy of theresulting bastnaesite/spinel composite material as a SO_(x)absorbent/catalyst. However, in seeking to find better ways ofphysically incorporating bastnaesite into such spinel matrix materials,applicant discovered certain processes whereby bastnaesite can bechemically reacted with the spinel-forming ingredients (e.g., alumina,magnesia, etc.)--as opposed to merely being physically associated (as amixture) with the spinel forming materials through the use of variouscatalyst binder materials.

Applicant then discovered that when bastnaesite is in fact chemicallyreacted with various metal oxide ingredients such as those which arecapable of forming a spinel (rather than being just mixed with them),there is a very dramatic increase in the SO_(x) absorbent and/orcatalyzing ability of the resulting bastnaesite/metal oxide materials.Having made this discovery, applicant then embarked upon a researchprogram aimed at comparing the SO_(x) absorbent/catalytic abilities ofthese bastnaesite/metal oxide materials with: (a) various metal oxidesalone, (b) spinel alone, (c) bastnaesite alone, or (d) physical mixturesof bastnaesite and spinel (considered both as mixtures of the differentparticle species and as mixtures of bastnaesite particles and spinelparticles which are bound together in composite particles through theuse of binder materials). This experimental program also establishedthat applicant's chemically reacted bastnaesite/metal oxide materialsmay be used to: (i) catalyze the oxidation of SO₂ to SO₃, (ii) absorbSO₃ and distinct SO_(x) catalyst species such as those formed by theSO_(x) catalytic activity of the same materials, (iii) absorb SO_(x)formed by other separate provided with cerium and vanadium (e.g., thosein the form of catalytically inert spinels which are impregnated withcerium or vanadium) and/or (iv) catalyze the reaction of the oxidationof SO₂ to SO₃ and cause it to be absorbed by other kinds of separate anddistinct catalysts such as alumino-silicate hydrocarbon crackingcatalysts (and especially so-called "bottoms" cracking catalysts).

The experimental evidence which established these findings will be givenin subsequent portions of this patent disclosure. For now, however,suffice it to say that the herein described processes improve upon thecircumstances and results associated with those processes described inthe 979 patent. For example, the desired "absence" of complex metaloxides within those spinels described in the 979 patent also can beobtained in the processes of this patent disclosure but without certainformidable drawbacks which are associated with the processes and/ormaterials described in the 979 patent. Of even more importance, however,is the fact that applicant has found that the herein describedbastnaesite/crystalline metal oxide materials are very good SO_(x)absorbents--even if they do in fact contain high concentrations of thosecomplex metals which the processes described in the 979 patent sought toavoid. Indeed, applicant often found that even if such undesired freecomplex metal oxide compounds are produced in applicant'sbastnaesite/crystalline metal oxide materials, and even if they exist inconcentrations greater than those permitted in the 979 processes (i.e.,in concentrations greater than 5% by weight), the herein describedbastnaesite/crystalline metal oxide materials still have SO_(x)absorbent activities which are much better than those exhibited by thespinels produced by the processes described in the 979 patent.

Having noted this, however, it now should be made clear that applicantalso has found that if the small sized spinel-forming ingredients calledfor in the 979 patent (i.e., less than 5 nanometers) are chemicallyreacted with bastnaesite, the resulting materials are often even moreeffective SO_(x) catalyst/absorbent materials than those made withlarger particles. In any event, the herein described processes, and theproducts made from them, are not hampered by the low particle densities,restrictive pH limitations and/or those catalyst regeneration problemsassociated with the presence of undesirable complex compounds (e.g.,free magnesium oxide, stoichiometric spinel) which detract from theSO_(x) absorbent performance of several prior art metal oxide basedSO_(x) absorbent/catalyst materials, including those spinels describedin the 979 patent.

The processes described in the present patent disclosure have some veryimportant economic advantages as well. For example, these processescompletely remove what is perhaps the most negative economic aspect ofthe processes taught in the 979 patent--namely, the strict requirementthat their spinel-forming ingredients (e.g., magnesia and alumina) haveparticle sizes of less than 5 nanometers. In other words, applicant hasfound that the 979 requirement that the ingredient particles be sized atless than 5 nanometers, can be completely obviated when comparablespinel-forming ingredients are chemically reacted with a bastnaesiteingredient--and thereby form a novel class of bastnaesite/metal oxidecompounds--rather than merely being physically mixed with them. Indeed,applicant has found that when bastnaesite is in fact chemically reactedwith spinel-forming ingredients (e.g., magnesia, alumina, etc.), all ofthe ingredients (including the bastnaesite) can have much largerparticle sizes. For example, alumina, magnesia and bastnaesite particlessized up to about 1,000 nanometers can be readily employed withoutsuffering adverse effects on the SO_(x) absorbent/catalytic abilities ofthe herein described bastnaesite/spinel materials. This is an extremelyimportant point because spinel-forming ingredients having particle sizesof less than 5 nanometers are much more expensive compared to chemicallyidentical ingredients having larger particle sizes. For example, aluminaparticles sized in the 20 to 1,000 nanometer range, and especially thosesized in the 60100 nanometer range, are far less expensive than the 2 to5 nanometer varieties called for in the 979 patent. It bears repeating,however, that negation of the particle size limitations of the 979patent is not to say that such smaller sized ingredients (i.e., thosesized at less than 5 nanometers) cannot be used in the presentprocess--but merely to say that their use is not mandatory. In otherwords, the smaller sized particles are less preferred for largelyeconomic reasons.

Finally, it also should be noted that the herein describedprocesses--like those described in the 979 patent--are applicable tosynthesis of materials which can be used for purposes other than removalof SO_(x) from FCC units. For example, the bastnaesite/metal oxidematerials produced by the processes of the present patent disclosure maybe employed in: (1) the production of spinel/crystalline metal oxidematerials used for catalysis of other reactions (e.g., petroleumprocessing reactions such as: (i) naphtha reforming, (ii) steam, methanereforming, (iii) hydrotreating and hydroprocessing, (iv) dehydrogenationcatalysts, (v) methane coupling, (vi) oxidative dehydrogenation and(vii) oxidation of propylene, (2) bastnaesite/crystalline metal oxideparticles which are especially adopted for use in admixture with othertotally different kinds of catalyst particles (e.g., hydrocarboncracking catalysts such as those alumino silicates and amorphousaluminas used in making so-called bottoms cracking catalysts) in orderto absorb any SO_(x) which is incidentally produced by a catalyst whoseprincipal duty is to catalytically crack hydrocarbons and (3)bastnaesite/crystalline metal oxide materials having propertiescompletely different from catalytic properties (e.g., superconductivityproperties).

SUMMARY OF THE INVENTION

In their most fundamental terms, the processes of this patent disclosureserve to chemically react bastnaesite with at least one metal oxidematerial in order to form certain novel bastnaesite/metal oxidecompounds wherein the bastnaesite and/or at least a component ofbastnaesite and at least one metal oxide material are chemicallyreacted. Applicant has opined that the exact nature of this chemicalreaction is one wherein a La₂ O₃ component of the bastnaesite becomes apart of the crystalline structure of a spinel-like component of theresulting bastnaesite/metal oxide product. Such materials areparticularly useful as SO_(x) absorbent/catalyst materials. Bearing inmind the previous discussions regarding the loose nature of thenomenclature associated with the term "bastnaesite", applicant canfurther identify their end product materials through use of thegeneralized formula: (Ce,La)OF/R₂ ²⁺ O R₂ ³⁺ O₃. Of all the materialswhich potentially fall within this definition, those which are basedupon bastnaesite/magnesia/alumina (i.e., (Ce,La) OF/MgO/Al₂ O₃), are ofprimary importance. This patent disclosure also is particularlyconcerned with using the herein described materials as SO_(x)absorbent/catalyst materials: (1) in their own right, (2) in chemicallyand/or physically-bound conjunction with known SO_(x) catalysts such asvanadium and cerium and (3) in conjunction with other totally differentkinds of catalysts such as those aluminosilicate catalysts commonly usedto "crack" crude petroleum. The bastnaesite/metal oxide compounds may bemade in various physical forms, e.g., FCC microspheroidal particles,large pellets of the type typically employed in so-called "fixed bed"catalytic systems and the like.

The most general processes for making the herein described materialswill comprise: (1) dispersing a R₂ ³⁺ B! compound such as alumina (Al₂O₃) in a liquid media (such as water) which also contains between about1.0 and about 10.0 milliequivalents of a monoprotonic acid (e.g., nitricacid, formic acid, acetic acid, etc.) per gram of the R₂ ³⁺ component ofthe R₂ ³⁺ B! compound (e.g., per gram of aluminum in Al₂ O₃) in order tocreate a R₂ ³⁺ B! sol material (e.g., an alumina sol); (2) mixing a R²⁺A! compound such as magnesia (MgO) with the R₂ ³⁺ B! sol material andthereby creating a R²⁺ A!/R₂ ³⁺ B! gel composition (e.g., amagnesia/alumina gel composition); (3) adding a bastnaesite material(e.g., a (Ce,La)OF material) to the R²⁺ A!/R₂ ³⁺ B! gel composition andthereby creating a bastnaesite/R²⁺ A!/R₂ ³⁺ B! total reactioncomposition; (4) spray drying the bastnaesite/R₂ ²⁺ A!/R₂ ³⁺ B! totalreaction composition in order to produce a solid solution material and(5) calcining the solid solution material resulting from the spraydrying in order to produce a solid solution of bastnaesite, R²⁺ oxide(e.g., MgO) and R₂ ³⁺ oxide (e.g., Al₂ O₃) i.e., producing abastnaesite/R²⁺ O/R³⁺ O₃ material (e.g., a bastnaesite/magnesia/aluminamaterial) having the generalized formula: (Ce,La)OF/R²⁺ O/R₂ ³⁺ O₃ or(Ce,La) OFF/nR²⁺ O/mR₂ ³⁺ O₃) and drive off, as gases, undesiredelements such as those contained in the A!, B! etc. components of theR²⁺ A!, R₂ ³⁺ B! ingredients (and/or in the mono-protonic acid and/or inthe liquid media) of the total reaction composition and therebyproducing bastnaesite/metal oxide materials (e.g., bastnaesite/MgO/Al₂O₃ materials) wherein at least a component of bastnaesite and at leastone of the metal oxide materials employed (e.g., MgO) are chemicallyreacted with each other.

Next, it should be noted that there are some particularly preferredembodiments of the abovedescribed process. One of these involves theadditional step of separately reacting a portion of the R²⁺ A!ingredient (e.g., MgO), with the bastnaesite and then adding theresulting bastnaesite/R²⁺ A! material (bastnaesite/magnesia) to a R²⁺A!/R₂ ³⁺ B! gel composition (e.g., to a magnesia/alumina gelcomposition). Expressed in patent claim language this preferred processwill comprise: (1) dispersing a R₂ ³⁺ B! compound such as alumina (Al₂O₃) in a liquid media such as water which also contains between about1.0 and about 10.0 milliequivalents of a mono-protonic acid per gram ofR₂ ³⁺ component in the R₂ ³⁺ B! compound (e.g., per gram of aluminum inalumina) in order to create a R₂ ³⁺ B! sol material (e.g., an aluminasol material); (2) adding a first portion of a R²⁺ A! compound to thebastnaesite material and allowing a resulting bastnaesite/R²⁺ A!material to age (e.g., from about 20 to about 180 minutes, andpreferably for at least 60 minutes); (3) adding a second portion of aR²⁺ A! compound (e.g., magnesia) to the R³⁺ B! sol material and therebycreating a R²⁺ A!/R₂ ³⁺ B! gel composition; (4) adding the resultingbastnaesite/R²⁺ A! material to the R²⁺ A!/R₂ ³⁺ B! gel composition tocreate a bastnaesite/R²⁺ A!/R₂ ³⁺ B! total reaction composition; (5)spray drying the bastnaesite/R₂ ²⁺ A!/R₂ ³⁺ B! total reactioncomposition in order to form particles and (6) calcining the particlesresulting from the spray drying in order to produce crystals of a solidsolution of bastnaesite, R²⁺ oxide (R²⁺ O) and R₂ ³⁺ oxide (R₂ ³⁺ O₃)i.e., producing bastnaesite/metal oxide materials having the generalizedformula: (Ce,La)OF/R²⁺ O/R₂ ³⁺ O₃ (or (Ce,La)OF/n R²⁺ O/mR₂ ³⁺ O₃)(e.g., (Ce,La)OF/MgO/Al₂ O₃) and drive off, as gases, any undesiredelements such as those contained in the A!, B! etc. components of theoriginal R²⁺ A!, R₂ ³⁺ B! compounds (and/or in the liquid media and/orin the mono-protonic acid) of the total reaction composition and therebyproducing bastnaesite/metal oxide materials wherein at least a componentof the bastnaesite and one or more metal oxide material is (are)chemically reacted with one another. Here again, the more preferredmaterials will be those wherein a component of the bastnaesite such asLa₂ O₃ is chemically reacted with a R²⁺ O component (e.g., MgO) of theresulting bastnaesite/metal oxide material. It also should be noted atthis point that applicant is of the opinion that the chemical reactiontaking place between the bastnaesite and a metal oxide is one wherein aL₂ O₃ component of the bastnaesite is transferred to the crystallinelattice structure of a spinel-like MgO Al₂ O₃ component of the overallbastnaesite/metal oxide material.

The most preferred embodiments of the herein described processes willemploy alumina as the R₂ ³⁺ B! ingredient and magnesia as the R²⁺ A!ingredient. The R²⁺ alumina is best employed according to a procedurewherein: (1) it is dispersed in a water solution containing from about5.0 milliequivalents of a monoprotonic acid per gram of aluminum in thealumina, (2) a magnesia-containing compound, and especially one whereinthe magnesia is in true solution, is mixed with the alumina dispersionto form a gel, (3) bastnaesite is added to the gel, (4) the gel is spraydried and (5) the product of the spray drying is calcined. An even morepreferred variation of this particular embodiment will be to: (1)disperse the alumina in a water solution containing 5.0 milliequivalentsof acetic acid per gram of aluminum in the alumina, (2) add aboutone-third of the magnesia compound which is being employed in theoverall process to a bastnaesite and age the resulting material for atleast one hour, (3) add the balance of the magnesia which is beingemployed in the overall process to the alumina in order to form amagnesia/alumina gel; (4) add the bastnaesite and magnesia mixture tothe magnesia/alumina gel, (5) spray dry the gel and (6) calcine theproduct of the spray drying.

Identity Of Ingredients

Applicant's processes may employ a wide variety of starting materials. Alist of such materials would include, but by no means be limited to,ingredients wherein: (i) a R²⁺ component is selected from the groupconsisting of magnesium, zinc, calcium, iron and manganese, (ii) a R₂ ³⁺component is selected from the group consisting of aluminum, cerium,iron, boron, manganese, lanthanum, chromium and the like (i.e., metalshaving like valances), (iii) the bastnaesite material is selected fromthe group consisting of naturally occurring bastnaesite, treatedbastnaesite (e.g., calcined and/or acid leached bastnaesite) orsynthetic bastnaesite-like materials (i.e., those having comparablemetal oxide components in comparable relative proportions to bastnaesiteminerals), (iv) the mono-protonic acid is selected from the groupconsisting of formic acid, acetic acid, or nitric acid and (v) theliquid medium is selected from the group consisting of water, analcohol, an ether, a ketone (specially acetone) and mixtures thereof.

The more preferred species of A! anions associated with the R²⁺ cationcan be selected from the group consisting of oxide, acetate,hydroxyacetate (which, incidentally, are particularly effective anionspecies for the practice of this invention), nitrate, hydroxynitrate,ethylate, ethoxide and mixtures thereof. The more preferred anionic B!species associated with the R₂ ³⁺ cation can be selected from the groupconsisting of acetate, hydroxyacetate (which here again are particularlypreferred), nitrate, oxide, hydroxide, hydroxynitrate, and mixturesthereof. Thus some of the most preferred starting materials mightinclude cation-anion combinations wherein the resulting R²⁺ A! compoundis selected from the group consisting of R²⁺ hydroxyacetate, R²⁺ acetateR²⁺ nitrate, R²⁺ oxide R²⁺ hydroxynitrate R²⁺ acetate, R²⁺ ethylate andthe R₂ ³⁺ B! compound is selected from the group consisting of R₂ ³⁺hydroxyacetate, R₂ ³⁺ acetate, R₂ ³⁺ nitrate, R₂ ³⁺ hydroxynitrate, R₂³⁺ acetate, R₂ ³⁺ hydroxide, R₂ ³⁺ oxide and the like. However, when allis said and done, the most preferred R²⁺ A! compound is a magnesium A!compound (e.g., magnesia) and the most preferred R₂ ³⁺ B! compound is analuminum B! compound (e.g., alumina.

It also should be noted in passing that in carrying out either the moregeneral embodiments of the herein described processes (wherein the R²⁺A! ingredient is not separately reacted with the bastnaesite) or incarrying out some of the more preferred embodiments (e.g., wherein aportion of the R²⁺ A! ingredient (e.g., magnesia) is separately reactedwith the bastnaesite and then added to a R²⁺ A!/R₂ ³⁺ B! gel), adi-protonic acid or tri-protonic acid may be used for certainhereinafter described pH adjustment purposes. Nonetheless, at least aportion of the acid employed to disperse the R₂ ³⁺ B! ingredient such asalumina--and preferably all of the acid used for this purpose--must befurther characterized by the fact that it is a mono-protonic acid.Moreover, the mono-protonic acid must be used in amounts such that itprovides an acid equivalency of from about 1.0 to about 10.0milliequivalents of mono-protonic acid per gram of R₂ ³⁺ in the R₂ ³⁺ B!ingredient (e.g., per gram of aluminum in alumina). Either organic,monoprotonic acids or mineral, mono-protonic acids, or mixtures thereof,may be employed for applicant's R₂ ³⁺ B! dispersion purposes. Thosemono-protonic acids which do not tend to leave residues upon decomposingunder the calcining conditions employed in the herein describedprocesses are particularly preferred. It is for this reason that the twomost preferred species of organic, mono-protonic acid are acetic acidand formic acid. For like reasons, the most preferred mineral,mono-protonic acid is nitric acid.

Milliequivalents Of Acid Ingredients

Upon discovering that the herein described processes are sensitive tothe number of milliequivalents of mono-protonic acid per gram of R₂ ³⁺in the R₂ ³⁺ B! compound (e.g., per gram of aluminum in alumina)--asopposed to the pH per se of the dispersion--applicant ran anexperimental program aimed at defining the range of this acidequivalency parameter. This program established that use of from about1.0 to about 10.0 milliequivalents of mono-protonic acid per gram of R₂³⁺ in the R₂ ³⁺ B! compound (e.g., alumina) give the best overallresults for a wide variety of starting materials. Use of at least 4.0milliequivalents and, even more preferably, use of about 5.0milliequivalents gave particularly good results for a wide variety ofR²⁺ A!, R₂ ³⁺ B!, bastnaesite ingredients--and especially forbastnaesite/magnesia/alumina total reaction compositions.

As a final comment on the subject of the nature of the acid(s) which canbe used in the herein described processes, it should be understood thatthe terms "pH" and "milliequivalents" ("meq") must be distinguished fromone another for the purposes of this patent disclosure. In order to makethis distinction, it may be useful to think of the term "pH" as meaningthe concentration of hydrogen ions (H+) per unit volume of acid. Next,it should be noted that, in many chemical reactions which are sensitiveto pH conditions, it usually does not matter what source of H+ions isused to create a given "pH"--that is to say that it does not matterwhether the "pH-producing" H+ ions come from a mono, di-, ortri-protonic acid source. This, however, is decidedly not the case withthe processes of this patent disclosure. For applicant's purposes, theconcept of "milliequivalents" of acid from a mono-protonic acid sourceis all important--and within a very wide pH range it does notparticularly matter what pH is created by the use of the 1.0 to 10.0milliequivalents of that mono-protonic acid which are used to carry outapplicant's R²⁺ B! (e.g., alumina) dispersion step. It also should benoted that those aluminas which applicant prefers for the practice ofthis invention also are characterized by the fact that they havedispersibilities in excess of 95% (and most preferably, greater than98.5%) when from 1.0 to 10.0 milliequivalents of a mono-protonic acid isused to disperse them.

For example, under the teachings of this patent disclosure, if applicantadded say a dispersible alumina to a solution having a pH of 3.0, therewould be no clear understanding as to what would happen if the "valence"of that acid were not also known (i.e., if it were not known whether theacid which created the 3.0 pH was a mono-protonic, di-protonic ortriprotonic acid). If the acid used to create the 3.0 pH were sulfuricacid, a typical di-protonic acid, the alumina would simply form a slurryand not a sol. That is to say it eventually would settle out and fail tocreate a material suited to the practice of this invention. On the otherhand, use of an appropriate amount of a mono-protonic acid such asnitric acid, would produce a usable alumina sol which in time wouldgel--and, hence, would be well suited for the practice of thisinvention. In other words, it should be understood that under theteachings of this patent disclosure, one could alter the pH of a totalreaction mixture, or the pH of the R₂ ³⁺ B! sol, by adding sulfuricacid, but still not produce a suitable total reaction mixture if aninsufficient amount (e.g., as was the case in Example 7 of this patentdisclosure) or an excess amount, of a mono-protonic acid were originallyused to create the R₂ ³⁺ B! sol. It also should be noted in passing thatthere are several commercially available R₂ ³⁺ O₃ materials (e.g.,alumina powders) that are already provided with acid(s). Consequently,in the case of those aluminas, which are already provided withmono-protonic acids, all one may have to do in order to make adispersion suitable for applicant's purpose is to add the overallalumina/acid material to a liquid media such as water and stir. In otherwords, if the acid already accompanying the alumina happens to be amono-protonic acid, and if this acid happens to provide sufficient acid"equivalents" to carry out applicant's processes, these aluminas needonly be mixed with a suitable liquid media such as water. If not,suitable amounts of a mono-protonic acids will have to be added to thealumina dispersion.

However, once the R₂ B! compound (e.g., alumina) is properly dispersedthrough use of a mono-protonic acid, composition, then various di-and/or tri-protonic acids (sulfuric acid as well as mono-basic acids)may be used to adjust the pH of the R₂ B! dispersion and/or the totalreaction composition. For example, once a given total reactioncomposition has been formed according to the teachings of this patentdisclosure, the pH of that total reaction composition may vary all theway from about 2.0 to about 10.0; and this pH range may be achievedthrough use of a very wide variety of mono, di or tri-basic acid(s).Indeed, even alkaline reagents can be used to make pH adjustments towardthe alkaline end of this pH range.

It also should be noted that in establishing these pH values, applicantgenerally found that if the pH of a total reaction composition fallsbelow about 2.0, dispersed R₂ B! particles, and especially dispersedalumina particles, tend to become dissolved into ionic forms. This isextremely detrimental to applicant's process and should be avoided. Italso should be noted in passing that alumina sol systems tend to becomevery viscous at pH values between about 6.0 and 8.0--but again tend tobecome less viscous at pH levels between about 8.5 and about 11.0. Next,it should be noted that the upper limit (11.0 pH value) is more in thenature of a practical limit rather than a technical one. This followsfrom the fact that the most preferred alkaline reagent for the practiceof this invention (if indeed one is used) is commercially availableforms of ammonium hydroxide which usually have pH values ranging betweenabout 11.0 and about 11.5. It also should be emphasized that certainmetal containing alkaline reagents such as sodium, lithium or potassiumhydroxide should not be employed to adjust the pH of any of applicant'sreaction systems since their metal components tend to "poison" theresulting catalyst materials.

Next, it should be noted that since the H+ions needed to disperseapplicant's R₂ ³⁺ B! ingredient (e.g., alumina) can be supplied bymono-protonic acids of differing acid species, and since each such acidspecies will have a different molecular weight, some further "internaladjustments" within applicant's 1.0 to 10.0 milliequivalent parameterwill usually be in order based upon certain other attributes of themono-protonic acid. For example, the molecular weights of the mostpreferred acids used by applicant in dispersing his R₂ ³⁺ B! ingredientsare:

    ______________________________________    NAME        FORMULA     MOLECULAR WEIGHT    ______________________________________    Formic      HCOOH       46    Acetic      CH.sub.3 COOH                            60    Nitric      HNO.sub.3   63    Hydrochloric                HCl         36.5    ______________________________________

Therefore, in order to supply the same number of H+ions from each ofthese different acid species, one would have to take into account themolecular weight of each acid. By way of a more specific example, itwould require 60 grams of acetic acid to supply the same number of H+ions as are supplied by 46 grams of formic acid. Applicant also notes inpassing that, in common chemical parlance, the molecular weight of suchan acid is often regarded as one equivalent of acid; and if it is amono-protonic acid, this amount is assumed to contain one equivalent ofH+ ions. Thus, quantitatively speaking, a milliequivalent of such anacid, at least for the purposes of this patent disclosure, could bethought of as the weight of mono-protonic acid×1000/molecular weight ofthat acid. Thus, if one always uses the same acid, one might simplyspecify the grams of that acid per gram of aluminum in the R₂ ³⁺ O₃compound (e.g., alumina) as an "equivalent amount" and a thousand timesthat as a "milliequivalent" amount of that acid.

Another acid related concept which should be noted in regard toapplicant's concern for the concept of "acid equivalency"--as opposed topH--is the "strength" of an acid. Again, applicant is primarilyinterested in the number of H+ions which are used to disperse the R₂ ³⁺B! ingredient and not with the pH of that dispersion per se. In thisregard, another conceptual difficulty lies in the fact that acids differin the degree to which they disassociate in solution. For purposes ofillustration, one might consider two acids: acetic acid and nitric acid.The equilibrium set up between these two acids and their ions are asfollows:

    ______________________________________           CH.sub.3 COOH ⃡ H+ + CH.sub.3 COO.sup.-           HNO.sub.3 ⃡ H+ + NO.sub.3.sup.-    ______________________________________

Next, it should be noted that one could have exactly the same number ofmilliequivalents of each acid, but since acetic acid is a so-called"weak" acid; a large proportion of its CH₃ COOH component co-exists withthe H+ ion and the CH₃ COO (acetate ion). On the other hand, practicallynone of the HNO₃ of nitric acid co-exists with the H+ion and the NO₃ ⁻(nitrate ion); hence, it is regarded as a "strong" acid. Thus for thesame number of milliequivalents of acid the nitric acid will supply moreH+ ions to the alumina than will be supplied by acetic acid.Unfortunately there is no easy way of accurately quantifying this"strength" effect. Hence, for the purposes of this patent disclosure,applicant must rely upon the 1.0 to 10.0 milliequivalent parameter tomake adjustments for the strength of the mono-protonic acid employed. Ingeneral, however, applicant has found that for the purposes of theirprocesses, nitric acid and hydrochloric acid are usually about two orthree times more effective than acetic acid in their ability to dispersea R₂ ³⁺ B! compound such as alumina. That is to say that, in performingthis dispersion function, about 1 meq of nitric acid or hydrochloricacid gives about the same effect as about 2.0 to 3.0 meq of acetic acid.By way of yet another example, applicant has found that formic acid'sability to disperse alumina is somewhere between that provided by a"weak acid" (acetic acid) and a "strong acid" (nitric acid).

In dealing with certain dispersible R₂ ³⁺ O₃ compounds, and especiallydispersible aluminas, it is important to appreciate that the number ofH+ ions (and to some extent their concentration) not only influences theviscosity of the resulting sols, it also will, to varying degrees,influence the size of the clusters and the rate at which the sols gel.As a final note with respect to the use of mono-protonic acidingredients, applicant would point out that once the identity of the R²⁺A! and R₂ ³⁺ B! ingredients is established (e.g., magnesia and alumina),the interaction of the particular materials with bastnaesite can be evenfurther encouraged by use of certain specific mono-protonic acids. Forexample, applicant has established that acetic acid is particularlyeffective in creating magnesia/alumina total reaction compositions.

Theoretical Suppositions

Applicant has opined that the reason why use of a mono-protonic acidproduces effective SO_(x) absorbent/catalyst materials while use of di-or tri-protonic acids does not, is that a mono-protonic acid creates achemical environment wherein a La₂ O₃ component of bastnaesite is morereadily transferred from the lattice of the bastnaesite to the latticeof at least one metal oxide material which makes up the final productmaterial. One highly plausible explanation for the dramatic improvementsin the ability of the herein described materials to absorb and/orcatalyze SO_(x) seems to be that once a lanthanum component (e.g., asLa₂ O₃) is removed from a bastnaesite lattice (and subsequently forms aR₂ O.La₂ O₃ compound such as MgO.La₂ O₃) the remaining bastnaesitematerial will have "voids" or "holes" in its crystalline structure.Applicant believes that the presence of such voids enable reactants suchas SO_(x) to come into contact (at the molecular level) with certainremaining components (e.g., ceria components of the bastnaesite) of aresulting bastnaesite/metal oxide material and/or of a resultingbastnaesite/metal oxide material and thereby those provide SO_(x)catalysis, SO_(x) absorbance and SO_(x) regeneration conditions whichmake these materials so useable as SO_(x) additives. To some extent,this reasoning is buttressed by several general observations. Forexample, applicant has noted that, in general, if a R²⁺ O compound(e.g., magnesia) is already intimately associated with a R₂ ³⁺ compound(e.g., alumina) when the R₂ ³⁺ sol is being created, transfer of La₂ O₃from the bastnaesite to the metal oxide will be much less pronounced.Concomitantly, applicant also found that a more effective, and hencemore preferred, way of effecting such a transfer of La₂ O₃ from abastnaesite lattice to a metal oxide lattice is by adjusting the acidequivalency conditions during preparation of their R₂ ³⁺ O₃ sol beforethe sol is mixed with the bastnaesite. Applicant's processes can usuallybe made even more effective when certain special steps are taken tocause the La₂ O₃ to be taken from the bastnaesite and transferred to theR²⁺ A! ingredient (e.g., to a magnesia component of the resultingmaterial). For example, this La₂ O₃ transfer appears to be especiallypronounced when a portion of the R²⁺ A! (e.g., magnesia) ingredient(e.g., from about 20 to about 40 weight percent, and most preferablyabout 33 weight percent of the R²⁺ A! ingredient), is reacted with thebastnaesite before that bastnaesite is associated with the R³⁺ B! (e.g.,alumina) ingredient.

Relative Proportions Of Ingredients

Applicant's primary"reactive ingredients" (i.e., R²⁺ A!, R³⁺ B! andbastnaesite) will, most preferably, constitute from about 10 to about 50weight percent of any given total reaction composition (i.e., thecomposition which is made up of the primary reaction ingredients plusthe liquid media and the acid(s) ingredients). It also should be notedthat the relative proportions of the primary reactive ingredients,relative to each other in the total reaction composition, will not equalthe relative proportions of the reactive ingredients in the end productmaterials i.e., in the bastnaesite/R²⁺ O/R₂ ³⁺ O₃ particles. Thisfollows from the fact that the liquid media and virtually all the acidingredient(s) are completely driven off during the spray drying andcalcining steps of the herein described processes. In any case, therelative proportions of the ingredients in a given total reactionmixture should be such that the bastnaesite will, most preferably,comprise from about 5% to about 50% of the final ingredients when theend products of this entire process are in their "dry" (i.e., calcined)final product, state (e.g., in the form of MS-FCC particles) The R²⁺ OR₂ ³⁺ O₃ (e.g., the MgO Al₂ O₃ component) of the overall bastnaesite/R²⁺O R³⁺ O₃ final product will if no other ingredients are used, constitutethe entire remaining 50-95 weight percent of applicant's final productmaterials. Any optional SO_(x) catalyst materials (such as ceria) whichbecome a part of the final product material should be used inproportions such that they constitute less than about 10.0 weightpercent of said final product material.

Any optional ingredients used to enhance the manufacturing process(e.g., viscosity agents, gas evolution agents, etc.), if any are used,may constitute from about 5 to about 25 weight percent of a given totalreaction mixture. More preferably, such optional production ingredients,if used, will constitute about 10% of a total reaction mixture. For themost part, those optional ingredients used to enhance the manufacturingprocess will be almost completely driven off by applicant's spray dryingand calcination steps. And, as yet another note on the subject ofrelative proportions, applicant would point out that, in general, themono-protonic acid ingredient(s) of the herein described processes willcomprise only from about 1.0 percent to about 10.0 weight percent of agiven total reaction mixture in order to achieve the 1.0 to 10.0milliequivalents requirement for practice of this invention. Thesemono-protonic acids will likewise be substantially driven off byapplicant's calcination step. This 1.0 to 10.0 weight percent range forthe mono-protonic acid does not, however, take into account any acidused to create certain soluble magnesia compounds such as magnesiumacetate which may be employed to create a Mg B! material wherein themagnesium is in true solution. Here again, however, any magnesiumacetate producing acid(s) would be completely driven off duringapplicant's calcining step.

The liquid media will constitute most of the remaining 50 to 90 weightpercent of the most preferred total reaction compositions. That is tosay that the liquid media will most preferably constitute 50 to 90percent of the total weight of: (1) the primary reactive ingredients(and optional ingredients, if any are used), (2) the mono-protonic acidand (3) the liquid media. Thus, for example, a total reaction mixturecontaining 40 percent by weight of reactive ingredients R²⁺ A!, R₂ ³⁺ B!and bastnaesite and 10 percent by weight of acid and volatile optionalingredients would, according to applicant's preferred proportions,contain 50% by weight of a liquid medium (or media) such as water,alcohol, etc. (if one neglects the weight of the relatively minoramounts of the mono-protonic acid ingredient in the total reactioncomposition). Again, making adjustments for the fact that most of theacid, most of the volatile optional ingredients (e.g., gas evolutionagent(s), viscosity agent(s), etc.) and virtually all of the liquidmedia are volatilized by the spray drying and calcination steps, andmaking further adjustments for the fact that the A! and B! components ofthe original R²⁺ A! and R₂ ³⁺ B! ingredients are replaced by oxygenduring the calcination process, an original total reaction mixturecomprised of say 10 weight percent of volatile, optional ingredient(s),10 weight percent bastnaesite, 40 weight percent metal oxide ingredientsand 50 percent water (and minor amounts of acid) would calcine to afinal "dry weight" product which is comprised of about 20 percentbastnaesite and about 80 percent metal oxide material.

By way of yet another example, if the primary reactive ingredients inthe example given above were 40% by weight of the total reaction mixtureand 50% of said reactive ingredients were bastnaesite, then theresulting total reaction mixture would be comprised of bastnaesite(20%), R²⁺ A! and R₂ ³⁺ B! (20%), optional and volatizable ingredients(10%) and liquid media (50%). This total reaction mixture would calcineto final product which contains about 50% bastnaesite, 25% R²⁺ A! and25% R₂ ³⁺ B! owing to the fact that essentially all of the otheringredients are ultimately driven off by the spray drying andcalcination procedures.

With respect to the subject of the relative proportions of theingredients, it also should be noted that applicant prefers to expresstheir R²⁺ /R₂ ³⁺ concentrations (e.g., magnesia/alumina) as the atomicratio of R²⁺ to R³⁺. Thus, in the case of a magnesia/alumina system,Mg/Al atomic ratio of 1.0 would be a 50% magnesia-rich material. In anyevent, applicant's experimental program established that the mostpreferred range of this R²⁺ /R₂ ³⁺ ratio is from about 0.5 (thestoichiometric ratio) to about 1.5 with ratios of about 1.0 being highlypreferred. Applicant would also note in passing that according to someteachings of the prior art--this ratio should not to be exceeded.However, applicant has found that with the use of chemically reactedbastnaesite, this higher value can be employed. Indeed, applicant oftenfound that the most preferred ratio is above 1.0.

Again, the preferred proportion range for the bastnaesite component ofthese materials is from about 5 to about 50 percent of the resultingbastnaesite/metal oxide material. The most preferred amount ofbastnaesite in the end product material will usually be about 33percent. When premixing the bastnaesite and R₂ O ingredient (e.g.,magnesia) and especially where the magnesium compound is in the form ofeither its acetate or nitrate, applicant also prefers to establish adesired ratio of the final product and then obtain that ratio in the endproduct by premixing from about 5 to about 50% of the total magnesiumemployed with the bastnaesite. Thereafter, the resultingmagnesium/bastnaesite composition is added to a composition comprised ofan aluminum compound (e.g., alumina) and the remaining magnesiumcompound.

Spray Drying Operations

Applicant's spray drying operations can be carried out by techniqueswell known to the catalyst production arts (e.g., those disclosed in the979 patent could very well be employed) to produce particles which areintended for use in FCC processes. For example such spray drying couldbe used to produce particles having a range of sizes such thatessentially all such particles will be retained by a Standard U.S. 200mesh screen and essentially all such particles will be passed by aStandard U.S. 60 mesh screen. Other physical forms of the end products(e.g., relatively large particles or pellets) also can be made--butthese larger particles have utility in certain select cases e.g., wherethe bastnaesite/crystalline metal oxide end product material is not usedin a fluidized catalytic process, but rather lies in a fixed bed throughwhich SO_(x) containing gas is passed.

Optional Drying Procedures

It should also be noted that in addition to a spray drying step,applicant's overall process may be enhanced by use of a separate anddistinct drying step which is carried out after the drying whichnaturally results from the spray drying step. For example, thoseadditional drying procedures taught in the 979 patent may be employed.Such additional drying may serve to better "freeze" the ingredients inthe homogeneous state in which they originally existed in the totalreaction composition. This additional drying will further serve toremove any remaining traces of the liquid medium which may be stillpresent in the interstices of the particles and/or associated with theparticulate product of the spray drying step (e.g., associated as waterof hydration). Drying times for this distinct drying step will normallytake from about 0.2 hours to about 24 hours at temperatures whichpreferably range from about 200° F. to about 500° F. (at atmosphericpressure), but in all cases, at temperatures greater than the boilingpoint of the liquid medium employed (e.g., greater than 212° F. in thecase of water).

Calcining Procedures

After such drying or desiccation--if such a step is employed--it remainsonly to take the solid matrix of the anhydrous particles produced by thespray drying and convert the R²⁺ and R³⁺, etc. components of the R²⁺ A!and R₂ ³⁺ B! ingredients to their oxide forms, e.g., R²⁺ O, R₂ ³⁺ O₃,etc. by a calcination step. In effect, the calcination step serves todrive off the A! and B! components and replace them with oxygen andthereby produce a final product having only the oxide forms of the R²⁺and R³⁺, etc. ingredients. The calcination step also serves to driveoff, as gaseous oxides, all but the "desirable" components of theresulting bastnaesite/crystalline metal oxide materials. For example,this calcination step will drive off the liquid media, acid, viscosityagent and gas evolution agent components of a total reaction mixture.Such calcination is readily accomplished by heating the products of thespray drying step--or of the optional desiccation step--at temperaturesranging from about 1,000° F. to about 2,000° F. (preferably atatmospheric pressure) for from about 60 minutes to about 240 minutes,and most preferably at about 1,350° F. for about 180 minutes. Thecatalyst particles should not, however, ever be raised to their meltingtemperatures.

Other Optional Procedures

As was previously discussed, one or more viscosity agents and/or gasevolution agents may be added to the original, total reaction mixture.Such viscosity agents may be used to help "freeze" the ingredients ofthe homogeneous distribution present in the original total reactioncomposition while the total reaction composition is undergoingvolatilization. In effect, such viscosity agents serve to inhibit theprocess reaction kinetics by raising a reaction mixture's viscosity andthereby decreasing the mobility of the reactive ingredient species whilethey are totally suspended in the liquid phase of the total reactioncomposition. In other words, such materials can provide those totalreaction compositions which are undergoing volatilization with a betteropportunity to form a solid matrix before certain undesired chemicalreactions (e.g., formation of stoichiometric spinel) can take place.Starch and/or gum arabic are particularly preferred viscosity agents forthis purpose. A wide variety of known gas evolution agents can likewisebe added to the total reaction composition to encourage evolution ofgases (e.g., those formed from the A! and B! ingredients) duringcalcination. Again, these viscosity agents and/or gas evolution agentswill be driven off by applicant's calcination step.

Other preferred variations of the herein described processes mayinclude: (1) use of nonorganic thickening agents such as alumina (i.e.,alumina used in addition to that alumina which may otherwise employed insay a magnesia, alumina, bastnaesite total reaction composition), (2)adjustment of the solids content of a reaction composition before it isfed to a spray dryer and (3) aging of the R₂ ³⁺ O₃ sol (e.g., aluminasol) before the sol is reacted with the other ingredients.

Finally, various metallic atoms, such as those of vanadium, cerium,platinum etc. also can be associated with the bastnaesite/crystallinemetal oxide materials produced by the processes described in this patentdisclosure. For example, this association can be achieved by adding thecomponents directly to the primary "reactive ingredients" (R²⁺ A!, R₂ ³⁺B! and bastnaesite) or by impregnating the bastnaesite/spinel productsof this patent disclosure after they are formed or by forming compositeparticles comprised of ceria-containing particles and bastnaesite/spinelparticles which are "glued together" through use of various catalystbinder materials well known to the catalyst production arts. By way of amore specific example of such techniques, vanadium pentoxide V₂ O₅, inoxalic acid, could be soaked into applicant's resultingbastnaesite/crystalline metal oxide materials. The resultingvanadium-impregnated bastnaesite/crystalline metal oxide material isthen re-dried at about 250° F. from about 60 minutes to about 240minutes and subsequently re-calcined for about 180 minutes at about1350° F. This calcination causes the oxalate to break down to CO₂ andsteam which are driven off as gases leaving the vanadium in the form ofcatalytically active VO₂ ⁺ ions. Bastnaesite/crystalline metal oxidematerials made by such impregnation techniques most preferably willcomprise from about 0.5 to about 4 percent vanadium by weight, withabout 2 percent by weight being a particularly preferred proportion.These proportions are generally applicable to the production of pelletsas well as FCC particles. However, since pellets are not as easily lostvia attrition, the pellets can be provided with higher concentrations(e.g., up to their economic--as opposed to technical limits) whichgenerally occur at about 10% by weight when very expensive material(s)such as platinum is employed as a SO_(x) catalyst.

Optional Goals Re: Concentrations Of Complex Metals

Even though it is by no means mandatory, one optional, and preferred,goal of the herein described processes is to produce bastnaesite/metaloxide materials having less than about 5% by weight of undesired complexcompounds such as free magnesium oxide and/or stoichiometric spinel.This is especially true in those cases where the material is to be usedas a SO_(x) absorbent and/or catalyst. Preferably, applicant'sbastnaesite/metal oxide materials will have even lower complex compoundconcentrations. Thus, for the purposes of this patent disclosure,applicant's use of expressions like: "virtually no" undesirable complexcompounds in the bastnaesite/crystalline metal oxide material or"substantially free of" such complex compounds, or expressions likebastnaesite/metal oxide materials having "no", "small amounts", "minimalamounts", etc. of such complex compounds generally can be taken to meanthose bastnaesite/crystalline metal oxide materials having less thanabout 5% by weight of such undesired complex metal oxide compounds.

However, having said this, it again should be strongly emphasized that,unlike the case of the spinel materials described in the 979 patent, theattainment of this 5% or less complex compound concentration is notessential to production of effective SO_(x) absorbent/catalyst materialsunder the teachings of the present patent disclosure. Indeed,bastnaesite/metal oxide materials having more than 5% by weight (and upto about 10% by weight) of such complex metal oxides will still fallwell within the teachings and/or spirit of this patent disclosure. Thatis to say that--in sharp contrast to the spinels described in the 979patent--bastnaesite/crystalline metal oxide materials having more than5% of such complex compounds are, nonetheless, very effective SO_(x)absorbent/catalyst materials. Indeed, applicant has generally found thatsuch bastnaesite/metal oxide materials are usually more effective thananalogous spinels having less than 5% complex compounds which areproduced by the processes of the 979 patent. It is also true, however,that those bastnaesite/crystalline metal oxide materials of this patentdisclosure which do, in fact, have less than about 5 % by weight ofcomplex compounds are often even better SO_(x) absorbent catalystmaterials than those bastnaesite/crystalline metal oxide materialshaving more than 5% of such complex metal oxide compounds. Indeed, acomparison of FIGS. 1 and 2 of this patent disclosure even suggests thatthe bastnaesite has in some way chemically reacted with "free MgO". Thatis to say that the free MgO peak of FIG. 1 has virtually disappearedfrom the XRD pattern of the material if it is chemically reacted withbastnaesite. This observation may be (or may not be) consistent withapplicant's theory that the most plausible chemical reaction takingplace is one wherein a La₂ O₃ component of the bastnaesite is reactingwith a magnesium oxide component of a spinel-like material. It alsoshould be noted that the relative SO_(x) additive performances of thetwo materials whose XRD patterns are depicted in FIGS. 1 and 2, asSO_(x) additives, also seems to bear out applicant's previously stated"bias" against the presence of complex compounds such as free MgO inSO_(x) catalysts in general.

It also should be emphasized that applicant's chemically reactedbastnaesite ingredient(s) may, or may not, become an integral part ofthe crystalline structure of the resulting bastnaesite/crystalline metaloxide material. That is to say that even though one or more ofapplicant's bastnaesite ingredient(s) (e.g., La₂ O₃) is (are) chemicallyreacted with one or more of the resulting materials' metal oxideingredients (e.g., MgO, Al₂ O₃, etc.), it (they) need not necessarilybecome an integral part of the resulting material's regular crystallinestructure.

At present, applicant's x-ray diffraction (XRD) data is inconclusivewith respect to the question as to whether or not any part of thechemically reacted bastnaesite (e.g., a La₂ O₃ component) becomes anintegral part of a regular, repeating unit within a given metal oxidematerial's crystalline structure; or conversely, whether such acomponent (e.g., La₂ O₃) is simply dispersed throughout the metal oxidematerial without becoming a part of its lattice structure--a la the wayin which "free magnesium" oxide is loosely distributed through aspinel's crystalline lattice structure when measures (such as thosetaught in the 979 patent) are not taken to prevent this kind of loosedistribution. In other words, it might be the case that the chemicallyreacted bastnaesite (or a component of the bastnaesite such as La₂ O₃)may be dispersed in a crystalline metal oxide without actually becominga regular repeating unit of the resulting material's overall crystallinestructure.

On the other hand, it also might well be the case that the bastnaesite(or a particular bastnaesite component such as La₂ O₃) forms a regularpart of a resulting metal oxide's (e.g., magnesia's) crystallinestructure within an overall bastnaesite/metal oxide material. Again, atpresent, applicant is of the guarded opinion that the chemical reactionwhich has taken place is essentially a chemical reaction between thebastnaesite and the R²⁺ O component (e.g., MgO) of the overall metaloxide component of the resulting bastnaesite/metal oxide material; butapplicant has not completely ruled out the possibility of a reaction ofthe bastnaesite with the R₂ ³⁺ O₃ component (e.g., Al₂ O₃) or a reactionof the bastnaesite, or a particular component thereof, with an entireR²⁺ O/R₂ ³⁺ O₃ (e.g., MgO/Al₂ O₃) crystalline metal oxide component ofthe overall material. Be all this as it may, a great deal ofexperimental evidence (e.g., X-ray diffraction, thermogravimetric andfluid catalytic cracking pilot plant) clearly shows that a chemicalreaction of some kind has in fact taken place between the bastnaesiteand at least one metal oxide ingredient (e.g., magnesia or alumina)and/or with an overall crystalline metal oxide molecule (e.g., amagnesia/alumina crystalline material).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a XRD pattern for a spine1 material wherein the Mg/Alatomic ratio equals one.

FIG. 2 depicts a XRD pattern for a material made with the spinel whoseXRD pattern is depicted in FIG. 1, when that spinel is chemicallyreacted with bastnaesite according to the procedures of this patentdisclosure to form a bastnaesite/metal oxide compound according to theteachings of this invention.

FIG. 3 is a XRD pattern for a bastnaesite/spinel compound made with analumina starting material having particles sized at 1000 nanometers.

FIG. 4 is a plot of XRD intensity ratios for two preparations (a ceriaimpregnated spinel and a bastnaesite/spinel compound) made with aluminasol ingredients prepared with differing amounts of milliequivalents ofacid/gm of aluminum.

FIG. 5 depicts the comparative SO_(x) absorption performance of a spinelwhich is impregnated with a ceria SO_(x) catalysts, versus abastnaesite/spinel compound made according to the teachings of thispatent disclosure.

DESCRIPTION OF PREFERRED EMBODIMENTS Chemically Reacted ExperimentalProgram Re: The Nature And Use Of Bastnaesite/Crystalline Metal OxideMaterials

Applicant's various experimental programs established: (1) that achemical reaction has in fact taken place between the bastnaesite andone or more metal oxide ingredients (e.g., R²⁺ O and/or R₂ ³⁺ O₃) usedin these processes--or between the bastnaesite and an entire crystallinemetal oxide component of the overall bastnaesite/metal oxide material(i.e., with a R²⁺ OR₂ ³⁺ O₃ component such as MgO Al₂ O₃), (2) that thepresence of complex compounds such as free magnesium oxide,stoichiometric spinel, etc. in the resulting bastnaesite/crystallinemetal oxide materials is not in any way detrimental to the SO_(x)absorbent/catalyst capabilities of these materials (e.g., relative tothose of the spinels taught in the 979 patent) but, nonetheless, shouldbe minimized for even greater effectiveness of the herein describedmaterials as SO_(x) absorbent/catalyst materials, (3) that matriceswherein bastnaesite and crystalline metal oxide materials are merelymixed together, or "glued" together through the use of a catalyst bindermaterial (as opposed to being chemically reacted), are far lesseffective as SO.sub. x absorbent/catalyst materials compared toapplicant's bastnaesite/crystalline metal oxide materials wherein thebastnaesite is in fact chemically reacted with at least one metal oxidecomponent of the resulting material, (4) very significant comparativeadvantages of applicant's materials over a wide variety of prior artmaterials re: SO_(x) absorbance and/or catalysis, (5) the ability ofapplicant's bastnaesite/crystalline metal oxide materials to act asseparate and distinct catalysts in chemical reactions other than SO_(x)absorption/catalysis reactions, (6) the ability of the herein describedbastnaesite/metal oxides to catalyze the oxidation of SO₂ to SO₃ andcause it to be absorbed by other entirely different catalysts (e.g., byalumino-silicate hydrocarbon cracking catalysts), (7) the nature andrange of the acid equivalency conditions which can be employed toachieve reactions between bastnaesite and the other ingredients e.g.,R²⁺ A! and R₂ ³⁺ B!, (8) the probable nature of the chemical reactionbetween the bastnaesite and a metal oxide the probable transfer of La₂O₃ from the lattice of the bastnaesite to the lattice of a resultingmetal oxide component of the overall resulting material--and mostprobably to the lattice of a R₂ O (e.g., MgO) component of an overallR²⁺ O R₂ ³⁺ O₃ (e.g., MgO Al₂ O₃) component of the resultingbastnaesite/crystalline metal oxide material and (9) the ability of theherein described bastnaesite/spinel materials to perform an SO_(x)additive function when they are mixed with other catalysts--either inthe form of particle mixtures or in the form of composite particles.

Representative TGA Tests

Measurement of the absorption rate of SO_(x) on various experimentaladditives was accomplished by a modified thermogravimetric analysis unit(TGA). The equipment used in such tests consisted of a PolymerLaboratories STA 1500® thermogravimetric unit coupled with amicrocomputer. Generally speaking, approximately 10 milligrams of agiven sample was loaded into a porcelain sample boat and heated undervarious conditions. SO_(x) pick-up was normalized to the weight at thepoint where SO_(x) gas commenced to be introduced. The composition ofthe SO₂ mix gas employed was usually 1000 ppm SO₂, 5% CO₂, 1% O₂, withthe balance being nitrogen. These TGA tests, together with a series ofexperiments carried out in a large scale FCC pilot plant established theusefulness of applicant's bastnaesite/metal oxides (e.g.,bastnaesite/spinel materials) in removing SO_(x) from flue gas of a FCCregenerator and/or their ability to be "regenerated" for sustained usein FCC units. When considered in conjunction with various X-raydiffraction measurements, these TGA and pilot plant tests have ledapplicant to the conclusion that a chemical reaction has occurredbetween the bastnaesite and the spinel; and that, in the absence of thisreaction, the otherwise very same ingredients would "age" or deactivatevery rapidly with respect to their SO_(x) absorbent/catalyst properties.

Before launching into a discussion of some of applicant's more importanttest results, it will be useful to better understand a few basic detailsconcerning the most important reactions which are taking place. To thisend, first consider the following chemical reactions:

    ______________________________________    (1) SO.sub.2 + 1/2 O.sub.2 → SO.sub.3 having rate R-1    (2) SO.sub.3 + MO → MOSO.sub.4 having rate R-2    (3) MOSO.sub.4 + H → MO + H.sub.2 S having rate R-3    ______________________________________

Next, it should be noted that in evaluating these chemical reactions,applicant was most concerned with determining the relative reactionrates of these processes. In practice, reactions (1) and (2) occur, atrates R-1 and R-2 respectively, in a FCC regenerator. Reduction reaction(3) occurs at reaction rate R-3, in a FCC reactor. Reaction (1) isconcerned with the conversion of sulfur dioxide to sulfur trioxide.Again, sulfur dioxide must be converted to sulfur trioxide before thesulfur content of a gas stream can be absorbed and removed from thatstream. Reaction R-2 is mostly concerned with the absorbance of SO₃ onceit is formed. Generally speaking, applicant found that the rate ofreaction R-1, the rate of the surface catalyzed oxidation of SO₂ to SO₃,is the "controlling" reaction in the above-noted reaction series. Forexample, in studying these different reactions, applicant found the R-2absorption rates are generally much faster than the R-1 catalysisreaction rate for the herein described materials (i.e., the absorptionrate is much faster than the rate of surface catalyzed oxidation of SO₂gas to SO₃ gas). In considering the details of these R-2 absorptionreactions, applicant also usually found that the overall "holdingcapacity" of a given SO_(x) absorbent material--rather than the rate atwhich the SO₃ gas reacts with that absorbent material--is the moreimportant factor.

The third reaction rate R-3 involves reduction of the metal sulphateformed in the SO_(x) absorbent material back to its metal oxide form(MO). Again, reaction (3) occurs in the FCC reactor--rather than in theFCC unit's regenerator unit. In any event, applicant has found that, ifreaction R-3 is slow, this implies that a "permanent" metal sulphate isformed in the SO_(x) catalyst. Consequently, the absorbent will declinein its ability to absorb SO_(x) --either through a loss of its abilityto absorb SO₃ or its ability to convert SO₂ to SO₃.

As part of their overall experimental program, applicant also providedcertain materials displaying a high rate of SO_(x) absorption with aseparate and distinct SO_(x) catalyst (e.g., cerium, vanadium) which wasknown to be capable of giving a high rate of oxidation of SO₂ to SO₃(e.g., they impregnated such materials with a cerium or vanadiumion-containing solution). For example, ceria particles or spinelparticles impregnated with ceria, were employed for such purposes.Applicant usually found that, as long as a SO_(x) catalysis rate (R-1)is kept high, even the less preferred SO_(x) absorbents were able tocapture a significant amount of the SO₃ (e.g., they captured more SO₃than those captured by prior art and/or commercially available SO_(x)absorbents).

FCC Pilot Plant Aging Studies

The FCC pilot plant employed by applicant consisted of a reactor, astripper and a regenerator. Catalyst was continuously circulated betweenthe reactor-stripper and the regenerator. In the reactor the circulatingcatalyst was contacted with a hydrocarbon feed stock. As a result of thereactions that occur on the surface of the catalyst, the so-called"cracking reaction", the catalyst becomes fouled with a deposit of"coke" which also contains a sulfur contaminant. The coked catalystpasses to a stripper where it is contacted with steam to removeentrained hydrocarbons. The stripped catalyst then flows to theregenerator where it is contacted with air to burn off the coke depositin order to restore the catalyst activity. It is at this point thatsulfur, which is part of the coke deposit, is burned to sulfur dioxide.As part of these experiments, the sulfur dioxide in the flue gas wascontinuously recorded by a SO_(x) analyzer.

In a typical experiment conducted by applicant, a FCC pilot plant wasfirst started up with a catalyst that did not contain any additive thatwill remove SO_(x). After the unit operation had been stabilized and theSO_(x) content of the flue gas had been established, the additive to betested was injected into the circulating catalyst stream. The normalamount of additive used was one percent by weight of the catalyst in thecirculating inventory. The SO_(x) content of the flue gas was thenmonitored for a period of up to 48 hours. On the other hand, if theadditive failed to remove the SO_(x) in the flue gas, the experiment wasterminated in a few hours. Typically after an experimental additive wastested, a standard additive of known performance was tested at the sameconditions as the experimental additive. This was done since it was notalways practical to use the same hydrocarbon feed stock or catalyst forevery experiment.

Some typical pilot plant results are shown below:

                  TABLE I    ______________________________________    SAMPLE DESCRIPTION                      SO.sub.x REMOVED, % wt    ______________________________________    Ceria/Spinel      90    Chemically Heated 92    Bastnaesite/Spinel    Ceria/Spinel      80    Physical Mixture of                      10    Bastnaesite/Spinel    ______________________________________

Suffice it to say that applicant repeatedly found that the SO_(x)performance of the materials produced by the herein described processesis comparable to far more expensive SO_(x) absorbent/catalyst materialssuch as ceria impregnated spinels. Applicant's chemically reactedbastnaesite/spinel materials also were much more effective SO_(x)additives than physical mixtures of bastnaesite and spinel. This factbecomes apparent after running such bastnaesite/spinel mixtures throughmany absorption/regeneration cycles. In order to more fully study thiseffect, applicant ran a series of hereinafter described, large scale FCCpilot plant tests wherein a wide variety of SO_(x) absorbent/catalystsmaterials were repeatedly used and regenerated.

By way of another method of presentation of this kind of pilot plantdata, FIG. 5 depicts the comparative SO_(x) absorption abilities of aceria impregnated spinel versus a chemically reacted bastnaesite/spinelmaterial which used the same spinel material. Both materials wererepeatedly used and regenerated over a 40 hour period. Such tests arebased upon SO_(x) "emissions" which are expressed as the kilograms ofSO_(x) emitted per thousand barrels of fresh feed stock materialprocessed in the FCC test unit. For example, the data shown in FIG. 5indicates that the curve for one of applicant's chemically reactedbastnaesite/spinel materials (i.e., curve A •--•--•) always lies justabove the curve for the ceria impregnated spinel (i.e., curve B Δ--Δ--Δcurve B) over the entire 40 hour time span of the test. This impliesthat applicant's SO_(x) absorbent performed almost as well as the farmore expensive, ceria impregnated spinel. It also should be noted inpassing that the expression "Baseline Emissions 100 Kg/mbbl" given inFIG. 5 is the designation for a rather arbitrary, but widely used,industry standard meaning that, for comparative purposes, one wouldexpect to get 100 kilograms of SO_(x) per thousand barrels of feedstockif no SO_(x) catalyst whatsoever were employed in the bulk FCC catalystinventory.

Next, it should be noted that some of applicant's other experimentsshowed that bastnaesite, by itself, shows little sustained ability toabsorb SO₃ after its first few passes through the FCC unit. For example,the material produced by the procedures of Example 7 (which arecharacterized by not having sufficient number of milliequivalents ofmono-protonic acid) gave poor long term results. In effect, thematerials produced acted as if they were physical mixtures ofbastnaesite and spinels rather than chemically reactedbastnaesite/spinel materials. It also should be noted in passing thatthe data for the processes described in U.S. Pat. No. 4,311,581 ("the581 patent"), tend to corroborate applicant's observations regardingbastnaesite's inability to be regenerated once it has formed a metalsulfate product with the SO₃ gas. For example, the 581 patent data showsthat 15% by weight bastnaesite had to be in the bulk catalyst in orderto give an 80% reduction in SO_(x). This stands in sharp contrast to theadditive described in Example 5 of this patent disclosure wherein an"average" of about 90% weight reduction in SO_(x) was achieved throughuse of a bulk catalyst using only 1% by weight of one of applicant'schemically reacted bastnaesite/spinel SO_(x) additives. Indeed, theSO_(x) additive whose performance is depicted in the --•--•-- curve ofFIG. 5 contained only 30% bastnaesite. Consequently, the concentrationof bastnaesite in the bulk catalyst inventory was only 0.3% as comparedto the 15% used in the process described in the 581 patent. This is atremendous difference. Thus, taken together, these various test resultsshow that while bastnaesite may have an excellent initial activity forremoving SO_(x), it ages very rapidly and it is only by using largeamounts (e.g., 15%) that bastnaesite can be made to continuously removeSO_(x) at acceptable rates for even relatively short periods of time.The X-ray diffraction data for the material produced by Example 7 alsostrongly indicated that the chemical interaction between the spinel andbastnaesite was minimal or even non-existent. Consequently, itsbastnaesite component aged very rapidly and lost its ability to convertSO₂ to SO₃. Thus, the overall SO_(x) removal efficiency for thismaterial was quite poor.

XRD TESTS

The techniques of X-ray diffraction (XRD) are of course well known.Hence, for the purposes of this patent disclosure, it need only bebriefly stated that the orderly, serried ranks of atoms in a crystallinelattice can be viewed at various angles in which files of atoms line upwith a clear "avenue of sight" along certain cutting planes. That is tosay that all crystals, in three dimensions, can be "viewed" from astandpoint of 3 different axes; and identification of such avenues canbe made by counting atoms spaced from an arbitrary point of origin alongeach of the three axes. Such a plane can be identified by 3 designatorse.g., A, B, C, or X, Y, Z, etc. having certain values 2, 5, 7, or 4,4,0(which, incidentally would be abbreviated "440") etc. In conductingx-ray diffraction tests, a subject crystal is rotated until a plane isobserved which permits X-rays of an appropriate wavelength to bediffracted by the lattice and, consequently, exhibit a detectable "peak"for such X-rays. The critical measurement for the x-ray diffraction peakplane is the angle of rotation of the crystal. In practice, because ofcertain mathematical relationships between these variables, such a peakis observed as an intensity ordinate plotted against an abscissa of 2theta, the angle of rotation. Thus, such x-ray diffraction patterns canbe thought of as exhibiting certain significant lines which correspondto the angle of rotation which is usually designated by the use ofexpressions such as interplanar spacing d(A) or 2-theta-d spacing or2-theta (e) or simply a "2-theta value".

In any event, x-ray diffraction measurements of this type were made byapplicant in order to test the degree to which desirable compounds(e.g., bastnaesite or bastnaesite derived compounds (e.g., La₂ O₃) or"undesirable" compounds (free magnesium oxide) were associated with agiven material's crystalline lattice structure. XRD tests also were usedin trying to establish the exact molecular structure of the end productmaterials made by the processes of this patent disclosure. That is tosay that various materials prepared by the processes of this patentdisclosure were studied by X-ray diffraction, both in their own rightand by comparison with other known production procedures and/or bycomparison with certain SO_(x) absorbent/catalyst materials obtainedfrom commercial sources. XRD evidence of this kind tended tocorroborate--but not conclusively prove--applicant's La₂ O₃ transfertheory. For example, it was noted that a large shift in the XRD,two-theta value of various materials was created by the herein describedprocesses. This shift seems to be due to a transfer of La₂ O₃ to thelattice of the subject material's R²⁺ O R₂ ³⁺ O₃ lattice system Thishypothesis also seems to buttress the results that applicant obtained inhis scanning electron microscope (SEM) experiments. In any case theseexperiments showed a significant amount of at least one rare earthelement (e.g., La) which was originally found in the bastnaesiteprobably had made its way into the crystalline metal oxide component ofthe end product material.

Applicant's overall experimental program also established that if astarting Mg/Al ratio for a given spinel material is known, and thetwo-theta value for that material is known, then applicant couldcalculate the amount of "free magnesia" in the end product spinelcomponent of the final product material. For example, applicant couldrelate the following cases:

                  TABLE II    ______________________________________    Starting               Mg/Al   Free    Mg/Al    Two-Theta     XRD     MgO % wt    ______________________________________    1.0      65.2°  0.5     18.7    1.0      64.5°  1.0     0    ______________________________________

In this example, a stoichiometric spinel was created which had a Mg/Alratio in the spinel of 0.5. The resulting material had a very prominentfree magnesia peak in its XRD pattern. On the basis of the knowledgethat the starting Mg/Al ratio was 1.0, the free magnesia was calculatedto be 18.7% by weight. In the second example of Table II, all of themagnesia was regarded as being in the spinel's crystalline lattice;hence, there was no "free" magnesia. Moreover, when applicant usedbastnaesite with these Mg/Al materials, he obtained similar peaks forthe spinel and free magnesia. They appear to be similar, for example: atypical material of this type gave the following XRD data.

    ______________________________________    Mg/Al    Two-Theta Mg/Al XRD    Free MgO % wt    ______________________________________    1.0      65.2°                       0.5          0    ______________________________________

Thus, with a two-theta value of 65.2°, applicant anticipated a largefree magnesia peak; however, the peak was essentially zero. Suchfindings constitutes very strong evidence that a new class of compounds(chemically reacted bastnaesite and spinel materials) have been producedby the herein described processes. This is to say that this data isstrong evidence that the bastnaesite and spinel have chemically reactedwith each other (as opposed to being only physically mixed with eachother). Taking into account other kinds of experimental evidence,applicant's interpretation of such XRD data is that magnesia has reactedwith a lanthanum oxide (La₂ O₃) component of the bastnaesite to form aspinel-like component, MgO.La₂ O₃, in the resulting material. Applicantalso tentatively concluded that the removal of the lanthanum oxide fromthe bastnaesite lattice has, in turn, most probably, made a ceriumoxyfluoride component of the bastnaesite more accessible, and hence moreable, to catalyze oxidation of sulfur dioxide to sulfur trioxide and toperform repeated cycles of SO_(x) capture and regeneration.

One problem in dealing with this XRD data, however, is that certainpeaks, such as free magnesia peaks, are not always zero. Moreover, withthe bastnaesite in the overall material, applicant's calculation of thefree magnesia became somewhat more tentative--especially whenconsidering results between the two extremes show in Table II. In anyevent, applicant dealt with this problem by expressing the free magnesiaas a ratio of the intensities of the spinel XRD peak to the freemagnesia peak.

FIG. 1 shows the X-ray diffraction pattern for a spinel. However, thespinel, by design, was not a particularly good spinel; that is to saythat it had a large amount of "free magnesia" and its spinel componentitself was a stoichiometric spinel--the material that generated thepatterns had a Mg/Al ratio equal to 1.0. In other words, it was exactlythe type of spinel that the 979 patent tried to avoid.

In any event, this XRD pattern is characterized by the presence of twodistinct peaks--one at about 62.5 for magnesia and one at 65.2 forspinel. The ratio of the intensity of the spinel peak to the intensityof the magnesia peak is 1.5. By way of comparison, FIG. 2 depicts a XRDpattern for a spinel with a two-theta value of approximately 65.2. Itwas generated by a starting composition which also had a Mg/Al ratio of1.0. However, the starting materials for the material whose XRD patternis depicted in FIG. 2 differ in that they also were chemically reactedwith bastnaesite according to the teachings of this patent disclosure.The difference in the magnesia peak intensity is very significant. Theratio of the intensity of the spinel peak to the intensity of themagnesia peak is, in this case, 6.5. That is to say that the freemagnesia is demonstrably lower (note the intensity of the peak at 62.5);moreover, the position of the spinel has not shifted. Taken togetherthese two facts indicate that a chemical reaction has occurred betweenthe bastnaesite and the free magnesia which, according to FIG. 1, wouldotherwise be present. The most probable significance of the observationthat the position of the spinel peak has not shifted implies that thefree magnesia has not simply entered into the lattice structure of thespinel but rather, has chemically reacted with the bastnaesite. That isto say that if the free magnesia had gone into the spinel lattice, thetwo theta value of the spinel would have shifted from 65.2 to 64.4. Thisobviously has not happened. On the other hand, if the two theta valuehad shifted to 64.4 then that would have meant that the bastnaesite hadnot reacted with the spinel. Be this XRD data as it may, the fact thatthe bastnaesite has reacted with the magnesia only takes on its realsignificance to this patent disclosure when this XRD data is coupledwith the fact that the bastnaesite is transformed into a regenerablecatalyst for the oxidation of sulfur dioxide into sulfur trioxide and/orthe absorption of SO₃.

FIG. 3 is a typical XRD pattern for a bastnaesite spinel made withCondea SB® alumina. The plot tends to corroborate applicant's findingthat excellent results were obtained when applicant used Condea SB®alumina which has 1000 nanometer alumina particles. Again, this factcontrasts sharply with the requirements of the 979 patent for use ofalumina particles sized at less than 5 nanometers. The magnesium peak isbarely discernible and the spinel/magnesia intensity ratio is 13.3. Thisfact also tends to support applicant's contention that at least somemagnesia is reacting with the bastnaesite. This evidence also suggeststhat, if the magnesia becomes too closely associated with the alumina asit does with the conditions emphasized in the 979 patent (wherein 2nanometer particles are employed), then a chemical reaction does notoccur between the spinel and the bastnaesite.

FIG. 4 is given to corroborate the fact that the milliequivalents ofmono-protonic acid used in preparing the alumina sols of this patentdisclosure is of paramount importance to the herein described 10processes. These milliequivalent parameters are expressed as theordinate in the plot given in FIG. 4. The abscissa is the ratio of thespinel peak to the free magnesia peak. For example, in FIG. 1 this ratiois 1.5 and in FIG. 2 it is 6.5. The plot in FIG. 4 also, in effect,shows that with a ceria-spinel, there is no effect produced by changingthe way the alumina is prepared relative to the amount of free magnesiain the SO_(x) absorbent. This finding is in agreement with previous workby applicant and others that showed that the ceria does not interactwith the spinel or the spinel ingredients. With applicant's use ofbastnaesite, however, just the opposite is true. As the milliequivalentsof acid used to prepare the alumina sol are raised, the amount of freemagnesia goes down and, consequently, the ratio of spinel to freemagnesia goes up. Again, this too is strong evidence that thebastnaesite is reacting with the magnesia in some way.

Applicant generally found that it is highly preferred to have the meqsof acid used in preparing an alumina sol above about fourmilliequivalents and most preferably in amounts providing about 5.0milliequivalents of such acid(s). The data in FIG. 4 also serves tocorroborate applicant's acid requirement parameters.

Other more specific variations on these processes also were established.For example, applicant found that by choosing the proper amount of meqof acid per gram of alumina in preparing certain alumina sols, the stepof separately reacting bastnaesite with a Mg A! compound such asmagnesium hydroxyacetate can be completely eliminated. In any case, themore preferred composition ranges that applicant arrived at as "norms"for the herein described SO_(x) catalysts which use of magnesia, aluminaand a supplemental SO_(x) catalyst (such as vanadium or ceria) are asfollows:

                  TABLE III    ______________________________________             Low        Optional High    ______________________________________    Magnesia   20           30       50    Alumina    25           39       50    Bastnaesite               10           33       50    Vanadia     2            3        5    Ceria       0            6       15    ______________________________________

COMPARISONS WITH CERTAIN PRIOR ART MATERIALS

Applicant conducted a great many tests aimed at comparing thebastnaesite/metal oxide materials (e.g., bastnaesite/spinel materials)produced by the methods of this patent disclosure with various prior artspinels and/or with bastnaesite alone and/or with various spinel-like ormetal oxide materials alone--with respect to their relative SO_(x)absorbent/catalyst capabilities. These comparative tests were based uponlaboratory TGA tests as well as large scale pilot plant tests. By way ofexample only, the results of some comparative, TGA tests are summarizedin TABLE IV.

                  TABLE IV    ______________________________________                   Two-     TGA    Sample Description                   Theta    SO.sub.x Absorption, %/Min    ______________________________________    Spinel         64.9     0.083    Spinel-Ceria   64.8     0.21    Bastnaesite Alone                   --       0.13    Unreacted      65.0     0.10    Bastnaesite And Spinel    Chemically Reacted                   65.2     0.16    Bastnaesite And Spinel    ______________________________________

Among other things, Table IV shows that the representative spinel testmaterial, by itself, displays rather low activity with respect to SO_(x)absorption (which is expressed in terms of a gain in weight of the testmaterial per minute). That is to say that, relatively speaking, the0.083 TGA value given in Table IV for the spinel indicates little SO_(x)absorbance. However, the next line of Table IV shows that when aneffective SO_(x) catalyst (e.g., ceria) is added to that same spinel,there is a very significant increase in SO_(x) absorption. In otherwords, the 0.21 TGA value represents a very significant increase inSO_(x) absorption relative to the 0.083 value for the spinel alone. Thiskind of data was obtained for many different spinel or spinel-like metaloxide materials. This fact forced applicant to conclude that, without aseparate and distinct SO_(x) catalyst such as ceria to convert sulfurdioxide to sulfur trioxide, very little SO_(x) is taken up by spinel (orspinel-like) materials because very little of the SO₂ is oxidized toSO.sub. 3 by a spinel alone. On the other hand, when the SO₂ is in factconverted to SO₃ (by the ceria), the spinel acts as a very goodabsorbent of the SO₃ gas which is produced. The only drawback to thisstate of affairs, is that the ceria used to effect the SO₂ oxidation isa rather expensive catalyst ingredient; moreover its presence in such asystem also requires a separate (and costly) process step for removingthe NO_(x) formed in the flue gas during applicant's calcination stepwhen ceria is present in the catalyst system.

Next, it should be noted that bastnaesite (as well as treatedbastnaesite materials)--by itself has significant SO_(x) absorptionactivity (in TGA tests), but only for the first cycle i.e., before"aging" becomes the factor that is only brought out by pilot plant testswhich involve the repeated use and regeneration of the test material.Moreover, applicant's experimental programs (TGA as well as pilot plant)repeatedly confirmed that a mere mixing of bastnaesite materials withspinel or spinel-like materials results in only minor improvements inthe SO_(x) absorption ability of the resulting particle mixture. Forexample, Table IV shows a value of 0.10 for such a mixture. As furtherevidence that a particular material behaves as a mixture of bastnaesiteand spinel (as opposed to a chemically reacted bastnaesite/spinelmaterial), one can calculate the weighted average of the contribution ofthe bastnaesite and spinel and obtain a value which is in virtuallyexact agreement with that measured for a bastnaesite particle, spinelparticle mixture. Again, all such unreacted materials showed very rapidaging in the FCC pilot plant tests. Applicant believes this is due tothe rapid aging of the bastnaesite and the resulting loss of the SO_(x)absorption function.

Be of this as it may, similar data was obtained for a wide variety ofbastnaesite/metal oxide materials having different R²⁺ A! and R₂ ³⁺ B!components and/or different relative proportions thereof. However,applicant invariably found that when bastnaesite is chemically reactedwith a metal oxide material very, very significant improvements are seenin the resulting bastnaesite/metal oxide material's ability to absorbSO_(x). For example, the 0.16 TGA value for the chemically reactedbastnaesite-spinel material shown in Table IV is significantly higherthan that of bastnaesite alone (even considered on a one time usebasis--as opposed to repeated use in a pilot plant (as depicted in FIG.5 of this patent disclosure), spinel alone or mere physical mixtures ofbastnaesite and spinel. Indeed, the 0.16 value for the chemicallyreacted bastnaesite/spinel material is close to the 0.22 value achievedby the cerium impregnated spinel. Hence, this data shows that virtuallythe same high levels of SO_(x) absorbance TGA values (e.g., 0.16 versus0.22) can be achieved at far less expense owing to the fact that ceriais a far more expensive material than bastnaesite. It also bearsrepeating that in some of applicant's FCC pilot plant experiments,applicant's bastnaesite/spinel materials actually gave better resultsthan many ceria-containing spinels.

Based upon this and a host of other experimental evidence, applicant hasconcluded that in the preparation of the bastnaesite/crystalline metalmaterials of the present patent disclosure i.e., those materialsobtained when bastnaesite ingredient(s) is (are) chemically reacted withmetal oxide ingredients, it is the occurrence of a chemical reactionbetween the bastnaesite and one or more metal oxides that creates SO_(x)absorbent/catalyst materials which are very effective in their abilityto convert sulfur dioxide to sulfur trioxide and, more importantly, intheir ability to absorb the sulfur trioxide once it isformed--regardless of the means by which it is formed.

Applicant also verified that, in the case of certain materials whichproved to be ineffective SO_(x) additives, a chemical reaction does notoccur between the bastnaesite and metal oxide ingredients. It also wasestablished that even though applicant produced excellent spinel-likematerials (some having the 64.6 two-theta value which were so prizedunder the teachings of the 979 patent), these "high quality" spinelswere not as effective catalysts for converting sulfur dioxide to sulfurtrioxide or for absorbing SO₃ relative to the bastnaesite/spinelmaterials of this patent disclosure--regardless of the "free" complexmetal content of the present bastnaesite/spinel materials. However, itshould be restated that these spinels when combined with ceria wereexcellent absorbents. Taken together, all of applicant's data imply thata chemical interaction has taken place between the bastnaesite (i.e.,one or more of its constituent components) and at least one of the metaloxide components (e.g., MgO) of an overall crystalline metal oxide, andthat it is the occurrence of this chemical reaction which enables theresulting bastnaesite/crystalline metal oxide material to act as both abetter SO_(x) catalyst and a superior SO_(x) absorbent relative to itsunreacted, constituent ingredients when they are used alone.

Next, attention again should be called to the fact that many of thespinel-like materials used in applicant's comparative experiments had atwo-theta value of 65.2 which, under the criteria used in the 979patent, would be considered poor spinels in terms of their SO_(x)absorbent abilities. Indeed, under the teachings of the 979 patent,spinels displaying such XRD readings were those having unacceptably highcomplex compound concentrations e.g., those having too much "free"magnesium oxide. Very surprisingly, however, such 65.2 two-theta spinelmaterials still made excellent SO_(x) absorption/catalyst materials whenthey were chemically reacted with bastnaesite. Applicant also verifiedthat such 65.2 two-theta spinel materials made rather poor SO_(x)absorbents when they were merely mixed with bastnaesite.

Those factors that made for "good spinels" in the 979 patent (i.e.,those having 64.6 XRD two-theta values), make less active SO_(x)additives when they are reacted with bastnaesite. Applicant'sinterpretation of this inconsistency with the teachings of the 979patent is that if the R²⁺ A! and R₂ ³⁺ B! components (e.g., magnesia andalumina) are too closely associated during the initial reaction phase ofpreparation (by virtue of the small particle sizes called for in the 979patent) they do not interact with the bastnaesite and that thispositioning results in a material that behaves more like a physicalmixture of, say, a spinel and a bastnaesite. Conversely, if such achemical reaction does occur, the resulting vacancies in the bastnaesitelattice probably make a remaining cerium oxyfluoride (CeOF) component ofthe bastnaesite material more available to the sulfur dioxide reactants.However, examination of the X-ray diffraction patterns for severalbastnaesite materials shows no "obvious" changes in the bastnaesite;nonetheless, applicant has used such methods in detecting very profoundchanges in the R²⁺ O/R₂ ³⁺ O₃ components (e.g., in spinel components) oftheir resulting bastnaesite/metal oxide materials.

Relationship To Hydrocarbon Cracking Catalysts

It also should be pointed out that applicant's thermogravimetric dataand applicant's pilot plant data often complemented each other to givefurther insights into the nature of the chemical reactions underconsideration. For example, in one set of comparative experiments,applicants' thermogravimetric data showed that bastnaesite, in and ofitself, acts as a good SO_(x) absorbent material--but only once (againsee Table IV). That is to say that as bastnaesite is repeatedly used asan SO_(x) absorbent and regenerated, its SO_(x) absorbent abilitiesdecrease dramatically. This effect was confirmed by applicant's pilotplant experiments which, by their very nature, were concerned withrepeatedly using, regenerating and reusing a given SO_(x) absorbentmaterial. This effect also was observed when bastnaesite particles aremerely physically mixed with hydrocarbon cracking particles (eithermixed as separate and distinct particle species or mixed withhydrocarbon cracking catalysts to form composite hydrocarboncracking/SO_(x) absorbent particles). This pilot plant data explains thefact that, when bastnaesite is used as a SO_(x) absorbent, largequantities of "make-up" bastnaesite must be continually added to thebulk catalyst of the FCC unit.

Applicant's comparative experimental program also established that manyprior art hydrocarbon cracking catalysts which are commonly used in FCCunits display some, albeit limited, ability to absorb SO_(x). This isprobably due to the widespread use of certain active forms of alumina inmost FCC hydrocarbon cracking catalysts. However, this inability toabsorb SO_(x) generally follows from the fact that there are no catalystmaterials in hydrocarbon cracking catalyst particles which are capableof converting sulfur dioxide to sulfur trioxide. In other words, manyhydrocarbon cracking catalysts could also serve to absorb SO₃ if acatalyst for converting SO₂ to SO₃ --such as that in applicant'sbastnaesite/spinel materials--also were used in conjunction with thehydrocarbon cracking catalysts. Several experiments confirmed that thisis indeed the case. When applicant's bastnaesite/metal oxide SO_(x)absorbent materials were in fact added to such hydrocarbon crackingsystems, it was found that a wide variety of FCC hydrocarbon crackingcatalyst-bastnaesite/spinel systems (and especially bottomscracking-bastnaesite/spinel systems) can then serve to absorb SO_(x) aswell as to perform their hydrocarbon cracking function if there issufficient capability to catalyze the conversion of SO₂ to SO₃.Applicant's material performs this function particularly well and canform the basis of overall catalyst systems comprised of a major amount(e.g., 95-99% by weight) of a hydrocarbon cracking system and a minoramount (e.g., 1-5% by weight) of applicant's bastnaesite/spinelmaterials. It also should be noted that, in various FCC uses ofapplicant's bastnaesite/spinel materials, the separate and distinctpresence of a SO_(x) oxidation catalyst species (e.g., cerium particlesor cerium impregnated particles) may be employed for the most economicutilization of all of the relevant materials. In any event, applicantfound that his bastnaesite/metal oxides SO_(x) additives can beassociated with a wide variety of other catalysts--e.g., with ceria,oxidation catalysts, hydrocarbon cracking catalysts (and especiallyso-called "bottoms product" cracking catalysts). Applicant also foundthat the herein described bastnaesite/spinel materials can be associated(e.g., by inclusion in the total reaction mixture before it is subjectedto spray drying or by mere mixing of applicant's bastnaesite/spinelmaterials with ceria impregnated spinel particles) with supplementalSO_(x) catalysts such as ceria, vanadia, etc. which SO_(x) oxidationcapabilities. That is to say that such SO_(x) catalysts (ceria, vanadia,etc.) are usually best added to a FCC unit as a separate particlespecies which is blended into the SO_(x) additive, but they may beincorporated directly into the bastnaesite/spinel materials described inthis patent disclosure.

A typical process for removing SO_(x) from a fluid catalytic crackingregenerator (wherein hydrocarbon cracking catalyst particles which arecontaminated by sulfur-containing coke), will comprise: (1) circulatinga minor portion of a bastnaesite/spinel, SO_(x) absorbent-catalyst witha major portion of a hydrocarbon cracking catalyst and wherein thebastnaesite/spinel, SO_(x) absorbent/catalyst is further characterizedby the fact that a bastnaesite component of the bastnaesite/spinel,SO_(x) absorbent-catalyst is chemically reacted with a metal oxidecomponent of said bastnaesite/spinel, SO_(x) absorbent-catalyst.

Further variations of such process can involve preferred embodimentswherein the bastnaesite/spinel, SO_(x) absorbent-catalyst is furthercharacterized by: (1) being a particle which is made into a compositewith separate and distinct SO_(x) catalyst particles, (2) beingparticles which are impregnated with a separate and distinct SO_(x)catalyst material selected from the group consisting of vanadium andcerium, (3) is used in particle admixture with bottoms-crackingparticles.

Other Preferred Uses of These Bastnaesite/Metal Oxide Compounds

This patent disclosure contemplates using the herein describedbastnaesite/metal oxide compounds as SO_(x) absorbent/catalysts inpetroleum cracking, chemical manufacturing and electrical powerproduction plants: (1) in their own right as SO_(x) additives, (2) inchemically and/or physically bound conjunction (e.g., as by impregnationtechniques well known to the art) with other known SO_(x) catalysts suchas vanadium, platinum and cerium, and (3) in conjunction with othertotally different kinds of catalyst particles and especially thosealumino-silicate catalysts commonly used to "crack" crude petroleum.

These bastnaesite/metal oxide compounds also can be used in variousphysical forms such as FCC microspheroidal particles, fixed bed pellets,etc. In accordance with one of the most preferred embodiments of thisinvention, bastnaesite/metal oxide compound(s) in the form ofmicrospheroidal particles will be introduced into a petroleum refiningFCC unit by blending them into a circulating bulk catalyst at someconvenient location in the FCC process. The amount of bastnaesite/metaloxide compound so added will vary with the individual FCC unit and withthe amount of SO_(x) desired to be removed from the unit's regeneratorflue gas. Generally speaking, the SO_(x) catalyst component of the FCCunit's bulk catalyst will be less than about 5.0% of the bulk catalyst(and more preferably they will constitute about 1.0-2.0 weight percentof the bulk catalyst).

Expressed in patent claim language, use of applicant's compounds in aFCC context can be described as removing SO_(x) from a fluid catalyticcracking process wherein hydrocarbon cracking catalyst particles, whichare contaminated by sulfur-containing coke, are regenerated by removalof the coke, said process comprising: (1) circulating a minor portion(e.g., less than 5.0% by weight of the bulk catalyst) of abastnaesite/metal oxide absorbent-catalyst with a major portion (e.g.,95 to 99 weight percent) of a hydrocarbon cracking catalyst and whereinthe bastnaesite/metal oxide SO_(x) absorbent-catalyst is furthercharacterized by the fact that a bastnaesite component of thebastnaesite/metal oxide SO_(x) absorbent-catalyst is chemically reactedwith a metal oxide component of said bastnaesite/metal oxide, SO_(x)absorbent catalyst.

Usually, in such FCC operations, the bastnaesite/metal oxide compoundparticles are added at a rate such that, of the total amount of catalystparticles and bastnaesite/metal oxide particles recirculating throughthe unit, 1.0 to 3 percent ("a minor amount") of the total catalystparticles will be bastnaesite/metal oxide compound SO_(x) additiveparticles. The average size of the SO_(x) particles introduced into suchFCC units will most preferably be the same as that of the bulk catalystparticles themselves, i.e., about 20 to 80 microns in diameter forpetroleum cracking catalysts.

By way of comparison, power production plants burning sulfur-containingcoal as well as various chemical and petrochemical plants, may prefer touse the herein described compounds in those pellet forms used inso-called "fixed bed" catalytic systems wherein a SO_(x) -containing gassuch as a flue gas is passed through a bed of catalyst pellets in orderto remove an SO_(x) component of the gas. In such cases those skilled inthis art will appreciate that two or more fixed beds may be operated insuch a manner that one or more bed(s) is (are) regenerated (e.g., byknown methods such as the use of hydrogen gas) while one or more otherbed(s) are being used as SO_(x) catalyst, absorbents.

When used in such fixed bed systems, the herein describedbastnaesite/metal oxide compounds need not have some of the attributesof those bastnaesite/metal oxide materials which are fluidized in FCCunits. For example, those bastnaesite/metal oxide compounds used infixed beds need not be as attrition resistant and need not have someparticular density as is the case for FCC use of the same materials.Moreover, such fixed bed pellets can be made in chemical formulationshaving higher relative proportions of bastnaesite/metal oxide compoundscompared to the binder or glue materials needed to make FCC particles.Generally speaking fixed bed pellets may comprise from about 5 to about90 weight percent bastnaesite/metal oxide compound and from about 10 toabout 95 weight percent binder material; and as in the case of the abovenoted FCC particles, the fixed bed pellets can be associated with knownSO_(x) catalysts such as vanadia, ceria, platinum and the like. Indeed,higher proportions (e.g., about 10% by weight) of these expensive, metalcatalyst materials can be used because far less material is lost fromthose non-fluidized systems.

PARTICULARLY PREFERRED PROCEDURES AND PREPARATIONS EXAMPLE 1

As part of their overall research program, applicant prepared manydifferent magnesium solutions which were thereafter used in theproduction of many different spinels. One particularly preferredmagnesium solution was formulated by adding 498 grams of glacial aceticacid to 554 milliliters of water. To the resulting mixture 167 grams ofmagnesium oxide (which was obtained from Combustion Engineering, Inc. inthe form of their MAGOX® product) was slowly added. The resultingmixture was then stirred until all of the magnesium oxide was dissolved.

EXAMPLE 2

Another highly preferred form of magnesium solution was prepared byadding 249 grams of glacial acetic acid to 803 milliliters of water. Tothe resulting mixture, 167 grams of magnesium oxide (obtained fromCombustion Engineering, Inc., in the form of their MAGOX® product) wasadded. The mixture was then stirred for thirty minutes.

EXAMPLE 3

Applicant also used magnesium oxide in slurry form. This was prepared byadding 167 grams of magnesium oxide (obtained from CombustionEngineering, Inc. in the form of their MAGOX® product) to 1052milliliters of water. The resulting slurry was mixed at high speed in aWaring blender.

EXAMPLE 4

Some of applicant's most preferred alumina ingredients were thoseprepared by hydrolysis of aluminum alcoholates. The crystallinestructure of these materials is best characterized as that of themineral boehmite (alpha alumina monohydrate). However, within this broaddefinition there is a whole host of solid aluminas and sols that may beused in the preparation of these materials (spinels) with bastnaesite.Applicant has found that a particularly effective alumina is Condea P-3®(obtained from Condea Chemie GMBH of Germany). Applicant has alsoprepared spinels with Grade SB® alumina (obtained from Condea ChemieGMBH). Other suitable aluminas similar to Grade SB are Catapal A®,Catapal B®, and Catapal C (which were each obtained from Vista ChemicalCompany). Within these general classes there also were several grades ofdispersible alumina powders that already had the required amount ofmono-protonic acid for dispersion mixed with the alumina. Hence, thesematerials were merely stirred with water to form alumina sols. By way ofexample, these aluminas are available as part of a class of aluminascalled "Disperal Special Aluminas"® from Condea Chemie GMBH of Germany,and as Dispal Alumina Sol from Vista Chemical Company. Another source ofalpha alumina monohydrate having a crystalline structure anddispersibility similar to the above-noted commercial alumina productsare the Versal Aluminas® obtained from the La Roche Chemical Company. Inpassing applicant would also note that one particularly preferred way ofpreparing an alumina sol is to add 25 grams of glacial acetic acid to1159 milliliters of water. To this mixture, 270 grams of Condea P-3®alumina powder was slowly added while stirring the mixture in a Waringblender. The mixture was stirred for twenty minutes.

EXAMPLE 5

One particularly preferred bastnaesite used in the preparation ofapplicant's total reaction compositions was Grade 4000®, Grade 4010® andGrade 4100® obtained from Molycorp, Inc. Grade 4000® is a unleachedbastnaesite mineral; by way of comparison, Grade 4010® represents abastnaesite which has been leached to remove alkaline earth metals;Grade 4100 has been both leached and calcined. Of these materials theGrade 4100 is somewhat preferred. It was prepared by slurrying it to 50%weight slurry and milling it to 2.0 microns in a sand mill.

Preparation Of Certain Preferred Bastnaesite/Spinel Total ReactionMixtures EXAMPLE 6

To 2154 grams of alumina sol (as described in Example 4), was added 846grams of magnesium acetate (as described in Example 1). The mixture wasthen stirred at high speed. To the resulting mixture 846 grams ofmagnesium oxide slurry prepared by the procedure in Example 3 was added.A slurry of bastnaesite (prepared as in Example 5) was added to themixture. The resulting slurry was spray dried and then calcined for onehour at 1350° F. The X-ray diffraction pattern for this material showeda two-theta value of 65.2. The ratio of spinel to magnesia was 6.5.Evaluation of this material on the TGA test showed an absorption of0.16%/min.

EXAMPLE 7

An alumina sol was prepared by dispersing 204 grams of Condea P-3®powder in an acetic acid solution containing 8.5 grams of glacial aceticacid in 884 milliliters of water. To this sol, 814 grams of magnesiahydroxy acetate (prepared as in Example 2) was added. The resultingmixture was stirred at high speed. To this mixture, 206 grams ofMolycorp Grade 4100® bastnaesite (prepared according to Example 5) wereadded and stirred at high speed. The resulting slurry was spray driedand then calcined for one hour at 1350° F. The X-ray diffraction patternfor this material showed a two-theta value of 64.6. The ratio of spinelto magnesia was 1.9. Evaluation of this material on the TGA showed anabsorption of 0.10%/min.

EXAMPLE 8

An alumina sol was prepared by dispersing 204 grams of Condea SB®alumina in an acetic acid solution containing 9.2 grams of glacialacetic acid in 982 milliliters of water. To this sol, 869 grams ofmagnesia hydroxyacetate (prepared as in Example 2) were added. Theresulting mixture was stirred at high speed. To this mixture, 221 gramsof Molycorp Grade 4100 bastnaesite (prepared according to Example 5)were added and stirred at high speed. The resulting slurry was spraydried and then calcined for one hour at 1350° F. The X-ray diffractionpattern for this material showed a two-theta value of 65.14. The ratioof spinel to magnesia was 4.3. Evaluation of this material on the TGAshowed an absorption of 0.16%/min.

EXAMPLE 9

A magnesia solution containing 13% weight magnesia was prepared byslurrying 119 grams of magnesia in 666 milliliters of water. To thisslurry were added 84 grams of glacial acetic acid. The resulting slurrywas added to 1150 grams of alumina sol prepared by the same formulationtaught in Example 7. The mixture was stirred at high speed. To themixture, 221 grams of Molycorp Grade 4100® bastnaesite (prepared as inExample 5) were added and stirred at high speed. The resulting slurrywas spray dried and then calcined for one hour at 1350° F. The X-raydiffraction pattern for the resulting material showed a two-theta valueof 65.04. The ratio of spinel to magnesia was 3.7. Evaluation on thismaterial on the TGA showed an absorption of 0.17%/min.

EXAMPLE 10

An alumina sol was prepared by dispersing 142 grams of Condea P-3®alumina powder in a solution of 2.9 grams of 70% weight nitric acid in718 milliliters of water. A solution containing magnesium nitrate wasprepared by dissolving 41 grams of magnesia in 174 grams of 70% nitricacid in 154 milliliters of water. This solution was added to the aluminasol and stirred at high speed. A slurry of magnesia in water wasprepared by adding 41 grams of magnesia powder to 167 milliliters ofwater. This was added to the alumina and magnesium nitrate mixture. Tothis was added 153 grams of Molycorp Grade 4100® bastnaesite preparedaccording to Example 5. The resulting slurry was spray dried and thencalcined for one hour at 1350° F. The X-ray diffraction pattern for theresulting material showed a two-theta value of 64.94. The ratio ofspinel to magnesia was 3.9. Evaluation of this material on the TGAshowed an absorption of 0.15%/min.

EXAMPLE 11

An alumina sol was prepared by dispersing 132 grams of Condea SB®alumina in a nitric acid solution containing 8.9 grams of 70% weightnitric acid in 539 milliliters of water. To this sol 390 grams of amagnesium nitrate solution were added; the magnesia content of thesolution was 20% weight. The resulting mixture was stirred at highspeed. To this mixture 72.8 grams Molycorp Grade 4100® bastnaesite(prepared according to the procedure in Example 5) were added andstirred at high speed. The resulting slurry was spray dried and thencalcined for one hour at 1350° F. The X-ray diffraction pattern for thismaterial showed a 2-theta value of 65.13. The ratio of the spinel tomagnesia was 13.3. Evaluation of this material on the TGA showed anabsorption of 0.16%/min.

EXAMPLE 12

An alumina sol was prepared by dispersing 188 grams of Condea P-3®powder in an acetic acid solution containing 8.5 grams of glacial aceticacid in 840 milliliters of water. To this sol 584 grams of magnesiumhydroxy acetate prepared according to the procedure in Example 2 wereadded. The resulting mixture was stirred at high speed. A mixture of 102grams of Molycorp Grade 4100® bastnaesite (prepared according to theprocedure in Example 5), and 288 grams of magnesium hydroxy acetate wereadded to the mixture of alumina sol and magnesium hydroxy acetate andstirred at high speed. The bastnaesite and magnesium hydroxy acetate hadbeen previously prepared and aged for one hour. The final slurry wasspray dried and then calcined for one hour at 135° F. The X-raydiffraction pattern for this material showed a 2-theta value of 64.82.The ratio of spinel to magnesia was 6.7. Evaluation of this material onthe TGA showed an absorption of 0.13%/min.

EXAMPLE 13

An alumina sol was prepared following the procedure in Example 4. To 431grams of this sol were added 338 grams of magnesium hydroxy acetateprepared according to the procedure in Example 2. The resulting mixturewas stirred to produce a uniform gel. This material was dried at 500° F.in a muffle and then calcined for one hour at 1350° F. The X-raydiffraction pattern for this material showed a 2-theta value of 64.93.The ratio of spinel to alumina was 2.0. Evaluation of this material onthe TGA showed an absorption of 0.08%/min.

EXAMPLE 14

An alumina sol was prepared following the procedure in Example 4. To 379grams of this sol were added 298 grams of magnesium hydroxy acetateprepared according to the procedure in Example 2. The resulting mixturewas stirred to produce a uniform gel. To this gel 44.4 grams of MolycorpGrade 5370 Cerium Nitrate were added and stirred to produce a uniformmixture. This material was dried at 500° F. in a muffle and thencalcined for one hour at 1350° F. The X-ray diffraction pattern for thismaterial showed a 2-theta value of 64.77. The ratio of spinel tomagnesia as 2.6. Evaluation of this material on the TGA showed anabsorption of 0.21%/min.

EXAMPLE 15

One of applicant's secondary criteria of "excellence" in a givenmaterial was the amount of complex metal produced in a givenbastnaesite/metal oxide material. In order to make such determinations,the starting compositions of various R²⁺ /R₂ ³⁺ metal oxide materialswere fixed at an atomic ratio of 1.0. This was done simply bymaintaining the ingredient composition of metal oxide-formingingredients at prescribed levels (e.g., 55.9% by weight Al₂ O₃ and 44.1%by weight MgO in order to produce a desired Mg/Al atomic ratio of 1.0)so that "acid equivalence" became the variable responsible for anyobserved differences in the character of any resulting bastnaesite/metaloxide material. The results of these tests showed that the hereindescribed processes showed that the acid milliequivalency range was 1.0to 10.0 with a 5.0 milliequivalency being especially preferred for anMg/Al atomic ratio of 1.0.

Thus, while applicant's invention has been described with respect tovarious scientific theories, specific examples and a spirit which iscommitted to the concept of the occurrence of a chemical reactionbetween the bastnaesite and one or more metal oxide materials, it is tobe understood that this invention is not limited thereto; but ratheronly should be limited by the scope of the following claims.

Thus having described my invention, what is claimed is:
 1. A method forremoving SO_(x) from a fluid catalytic cracking process whereinhydrocarbon cracking catalyst particles, which are contaminated bysulfur-containing coke, are regenerated by removal of the coke, saidprocess comprising: (1) circulating a minor portion of abastnaesite/spinel SO_(x) absorbent-catalyst with a major portion of ahydrocarbon cracking catalyst and wherein the bastnaesite/spinel, SO_(x)absorbent/catalyst is further characterized by the fact that abastnaesite component of the bastnaesite/spinel, SO_(x)absorbent-catalyst is chemically reacted with a metal oxide component ofsaid bastnaesite/spinel SO_(x) absorbent-catalyst.
 2. The method ofclaim 1 wherein the bastnaesite/spinel, SO_(x) absorbent-catalyst isfurther characterized by being a particle which is impregnated with aseparate and distinct SO_(x) catalyst material.
 3. The method of claim 1wherein the bastnaesite/spinel SO_(x) absorbent-catalyst is furthercharacterized by being a particle impregnated with a separate anddistinct SO_(x) catalyst material selected from the group consisting ofvanadium, cerium and platinum.
 4. The method of claim 1 wherein thebastnaesite/spinel SO_(x) absorbent-catalyst is used in the form of aseparate and distinct particle species.
 5. The method of claim 1 whereinthe bastnaesite/spinel SO_(x) absorbent-catalyst is used in the form ofparticles which are associated with hydrocarbon cracking catalystparticles in a composite particle through the use of a catalyst bindermaterial.
 6. The method of claim 1 wherein the bastnaesite/spinel SO_(x)absorbent-catalyst employs MgO.Al₂ O₃ as a metal oxide.
 7. The method ofclaim 1 wherein the hydrocarbon cracking catalyst is a bottoms-crackingcatalyst.
 8. The method of claim 1 wherein a separate and distinctSO_(x) catalyst species is circulated with the hydrocarbon crackingcatalyst and the bastnaesite/spinel SO_(x) absorbent catalyst.
 9. Themethod of claim 1 wherein a separate and distinct ceria impregnatedspinel species is circulated with the hydrocarbon cracking catalyst andthe bastnaesite/spinel SO_(x) absorbent catalyst.
 10. A method forremoving SO_(x) from a gas by passing said gas through a fixed bed of aSO_(x) catalyst/absorbent comprised of a bastnaesite/spinel compoundcharacterized by the fact that a bastnaesite component of thebastnaesite/spinel compound is chemically reacted with a spinelcomponent of said bastnaesite/spinel compound.
 11. The method of claim10 wherein the bastnaesite/spinel compound is further characterized bybeing a pellet which is impregnated with a separate and distinct SO_(x)catalyst material.
 12. The method of claim 10 wherein thebastnaesite/spinel compound is further characterized by being a pelletimpregnated with a separate and distinct SO_(x) catalyst materialselected from the group consisting of vanadium, cerium and platinum. 13.The method of claim 10 wherein the bastnaesite/spinel compound is usedin the form of pellets which are associated with other catalystmaterials selected from the group consisting of vanadium, cerium, andplatinum in a composite pellet through the use of a catalyst bindermaterial.
 14. The method of claim 10 wherein the bastnaesite/spinelcompound employs MgO.Al₂ O₃.